AFRICAN FRESIIWATER P l tAWNS O F 'I'IIIf SPECIES L'ARIDINA NILOTICA. 33

3. African Freshwater P rawns of tlie Species Ca~iil inu d o t i c u (Roiix), By I S A U E L L ~ GORDON, with Special Referencbc to tlio Nile Ba.jiii.

D.Sc., Pi1.D.'.

(Submitted for publication by permission of the Trustees of the British Museum.)

[Received November 5,1929 : Read February 18, 1930.3

(Text-figures 1-13.)

INTRODUCTION.

The present pa,per is the outcome of a strtdy of tlie freshwater pra.wiis hongl i t back by Mr. RI. Grdia.iii from hi8 Yisliing Survey of Lake Victoria, 1927-8, and by hfr. E. 13. Wortjhington (Fisliiiig Srirvey of Lakes Albert ant1 T

34 DR. ISABELLA GOBDON : AFRICAN FRESUWA'L'ER

t h a t of t h e shore form in several respects, ant1 t h k led t o a comparison of t h e rostrum i n all t h e African material ; this study forms the tliiid part of the paper.

The author wishes t o ackiiowletlge fier indebtediiess to I"3f. Ch. Gravier, of t h e Mus6um d'aistoire Naturelie, Paris, wlio sent for examination a number of specimens determined hy 13oiivier, iiiclutling- t,lie t?ypo-speciriiens of C. ufricuna var. egyptiaca Bouvier.

Part I.-TYPES O F 'I'ELSOY FOUND \YITTlIN TIlE SPECIES.

'L'he results of :LII ex:~inin;r.tioi~ of tlie telson in 433 specimens from Egypt a re given in Table I. 'I'ypicn.lly the apex of tlie telsoii is reliitively narrow and c h w n out into a n aciite median point. !L'liis point is occasionally absent, or may sometimes be replaced by a s1:oi.t spine. 1 7 1 212 spcciiiieiis (see Table I.) there a r e only fouv spines, a pair of sliort, subteimiiiial wies :i t id ii. pair of mnch longer terminal ones, a.s illrratrsted in text-fig. 1. St:t:c a r e often present on the inner

Text-figure 1. 'l'exLfigure 2.

I

Fig. I.-Apex of the tclfion of s C. ~ziloticn Y ~ P . lypicn from the Lower Nile-one of the most

Fig. 2.---Apex of the telson of a C. ?dot i in var. typica from tlie Lower Nile-another very characteristic forms. Csmcra lucida outlinc. X 100.

characteristic form. x 100.

margill of each terminal spine. In 167 specimens t h e posterior margin of the telsorr is wider, and tliere is, oil either side of the medimi poitit, an additional & Q l t spine :irnied on both sides with set= (text-fig. 2). Tliirty-seven specimens were :\Is0 of this type, bat, with one of tlie short adiiietlian spines absent (see 'j!;tk)le I.). Orily ten specimens from Egypt li:id a telson of tlie type represented i n text-fig. 3, btit this is the pretloriiinarlt. form in Lake Nyassx, Lake Ngami, and Natal. Wliere this forni pi,edomin:ttes another type, representeil in fig. 4, O C G I I ~ S , but i n niuch s~i,nlIer riiiinbe~~s, nntl t h t repi,eserit,ed in text-fig. 1 is absent. The types represented i n text-figs. 1 and 2 O C C I I ~ i n approxiinately equal numbers

PRAWKS OF THlC SPECIE AllIDtNA NlLOTICA

Text-figure 3.

35

Apex of the telson of a C. nilotica from Lake Nyassa. x 100.

I , I ext-figure 4.

Apex of the telson of a C . niloticn from River Umgeni, Natal. x 130. 3"

36 DR. ISABELLA GORDON : AFRICAN FRESHWATER

in Egypt, while t h e latter type appears t o preponderate in Lakes Albert and Victoria.

The niiniher of specimens from t h e affluerits of Lake Tangariyika (Calman, 1928) is too small to give any real itlen of t h e v:wiation exhibited by the telson, but, R.T: in Egypt, t h e same two forms occur in almost equal iiumbers.

Foiir specimens from Egypt liad a broad posterior border to t h e telson, brit :ill tlie spines were of the type characteristic of C. niloticcc (text-fig. 5 : cf. text3-fig. 6). This form of telssn is usually somewhat irregular, as text-fig. 5 tlernoiistr:i.tes, and i t is possible t h a t the posterior portion may have been regeiier.ited af ter some accident. The specimen from which text-fig. 7 was ot)l;tiiied has a long t~ostrum similar t o t h a t of C. izilotica var. typica,; t h e other specimens a re damaged and t h e rostrum is incomplete. These specimens a r e

Lext-figure 5.

d

A p m of tlie telson of a C t r d i n n from the Lower Nilc --probably an abnormnl C. i t i h t w i Tar. typicn. X 100.

:a + 1 Of ~

C9Z

801

:s + 1 8EP

............... suampads 30 'luao xad 'y

..................... suaqoads 30 'O

N

'2)

.+dL83 '1 s]

'9 'BY --------

.L+gv30T

38 DR. ISABELLA UORDON : AFRICAN FRESEWATER

process of mounting in Canada balsam. A t the junction of the two parts there is a structure resembling a chitinous plug. Only five specimens from Egypt had a telson of this type ; two specimens from a swampy river (Brikoba River) near t h e west shore of Lake Victoria also belong t o this group. These seven specimens have R rostruin which is shorter than is characteristic of C. izilotica var. t p i c a , and the spines on tlic dorsal margin extend to within a short distance of the apex (qf. text-fig. 13, a & b). Bouvier (1925, pp. 136 & 137), i n his key t o t h e c1:tssification of the species of Cffiridiw, includes C. i~frica?aa and part of C. ozilotica in t h e group with soies Iat6rales du telson beaacoup plus courtes qne les interm6diaires. These two species diEer, according t o this key, i n tlie ratio of dactylus to propodus of the fifth peraeopod ; i n C. ?LiZotica this ratio is approximately 1 : 4, in C. africa7ea it is almost 1 : 3. From Yable lI., 15, i t will be seen tha t the

Text-figure 6.

Apex of the tolson of s C. ufricni~a var. agyptiaca from the Lowor Nile. X 75.

propodus of perceopod v. is 2.85 t o 3.00 times t h e length of t h e dactylus in tlie specimens with telson as i n text-fig. 6, a.nd 348 to 3.75 i n the t>ypical C. nilotica. This suggested t h a t t h e seven specimens in question belonged to C. africana, and , on comparing them with t h e ty pe-specinlens of C. africnm var. cegyptiuca Bouvier, they proved t o be identical. The t>erminal setose spines of 13onviers type-specimens a.re simi1a.r in structure t o those represented in text-fig. 6, a.nd tlie se t8 extend t o t,he proximal portion of each spine ( c j . text-fig. 6, and Bouvier, 1925, p. 215, fig. 471). The five Egyptian specin~ens a re obviously immatme, and the striict,rire of t h e setose spines suggests that,, a t tlie next moult, tlie tlista.1 portion might be entirely cast off a.nd a form simi1a.r to t h a t represeiitt-d in text-fig. 5 result. B u t this is unlikely, for one of t h e specimens froni Bukoba River measures 25 inin. i n length and still bears the long setose spines on tlie telson. These long terniinal spines a re very characteristic of Bouviers Groupe clu C. afiicuna, which 6 se

PRAWNS OF THE SPb2IER CARIDIHA NILOTICA. 39

distingne de tous les nutres, snuf de ceIni d u C. typzcs, par Ies soies du teIson dont les intermkdiaires aoiit longues e t richement munies de barbules, les laterales e tant beaucoup plus courtes (Houvier, 1925, p. 212).

The most striking thing ahout C. africai~cc is i ts nppnrent rarity, for only 1.1 4 per cent. of the prawns from Lower Egypt * belorig to this species. The specin1en.t i n Mr. Grahxms collection are known to come from n swampy tributary, and not from Lake Victoiin itself; nothing is known at present about the exact localities of those from Egypt .

Text-figure 7 .

Apex of the telson of a specimen of C. ~ t i l o t i c n , measuring 5 mm. in length, from the open waters of Lake Victoria. X 230.

Text-fig, 7 represents t h e apex of Bhe telsori of a. specirneti meatsriring approximately 5 mni. in total leiigtli fvom t h e open wnt.ersof Lake Victoria. This specimen corresponds to post-1a.rval stage 11. (Gurney, 1927, p. 257), but the posterior border of the telson projects fur ther i i r the nieclian portion, which may represent the median point of t h e a l u l t telson, t h a n i t i Gurneys figure (1927, p. 258, fig, 62 D). Foriris sirnil:tr to Gurneys figure R S well as interniedinte forms also occur, and, as it isgenernlly the larger specimeris which ha\ e the most prominent median projection, this stage is pror)a.bly 211 intermediate pliase between the condit,iori represented in Gurneys figure a.nd the contlit~ion found in the adult. A young specimen of 6.35 mm. in total lengtli, when measured, agrees i n all essentials with the adults, i. e . , the dactyli of the tjhird t o fiftll perzopods are lorig and slender and the pRlm of each chelipetl is short. The ratio of length to breadth of dactylus and of length of finger to length of palm does not, therefore, appear to a.lter with the age or size of the specimens.

Q The percentages given in Table I. are calculated from the total 438, which includes the C. africnna material.

4u OH. IbABELLA GORDON : AVRICAN FRESHWATER

LAlt LL.-slUDY O F TUM ClIOttACIc hIlCNDAGES I N ~ b r ~ l t I A L FROM VARIOUS AFRICAN LOCALITIES.

l from blie complete tLbles of iiiensureinents, t h e lowest and tlie lrigliest ratios being given i n eecli inst:tiice. T n adtlition, tlics iiiiinbcr of clactylnr spines :rnd t h e size of tlic OVA aie giveii. Eighteen specimens f i o i i i vnrious localities in Llie Lower Nile varying iii leiigtli from 18.5 to 31 min. were inenstired, and the rniige fi,oni lowest to liigliest i z regarcled as cliaracteristic of tile typicd foriii of G. niloticn.

In tire Wnrtliingtoii Collt.ction the specimens fioiii i,lie Victoria Nile above Murclii>oii F~ l l s agree iri all p in t , , witli tlie Egyptiaii form, save t h a t the clnctylui of tlie f i f t l i ~ ~ e r ~ m l i o t i is sonie\n hat longer ni i t l iiarrower (see Table 11.). lii~fortiiiia,tely the t u h of bprciinens froin the Victoiin Nile below Murchisoii Falls liacl dried up, :mtl i t wai iiot possible to obtain satisfactory meiisurements. As far as could be judgecl these speciiriens agree with the typical Egyptnin form.

Text-figure 8.

Chelipeds 1 and 2 of lacustrine form of C. niloticrr. from the open waters of Lake Albert, The palm is shorter than in any other type from the whole Nile Basin. x 75.

Specirneiis from among sliore-weeds near Buliuka., Lake Albert, belong to G. ~iiZoticc6 mr. t~/i2licc~, but tlie ovii n i z a trifle smaller. Those froin ~IlalIow water (7 inetres bottom) near Bntiabn, Lakc Albert, are very different from the typical C. vLiZoticffi. Tlie ra.tio finger-length to pdm-length is niuch higher, therefore t h e palm is shorter in both chelipeds. Moreover, t h e tlnctyli of tlie tllird and fifth pert1 opods are longer a.iid niore slender, while the ratio of propodus-length tQ tla.ctylus-lengtli is s i d l e r . This form is not apparently quite tlie saiiie as t h a t known as C. wilotica var. gmcih1ie.s de n h r i from Celebes, for Kemp (1918, P. 276) gives t h e ratio of leirgth to breadth of clactplus* as 3.8 to 4.20 for perzopotl 3,

-a The length of the dactylns does not include the terminal claw, but is that of tho partilldicated by the broken line in text-figs. 11 and 12 ; the breadth measured is that ona level with (but not including) the upper or proximal dactylitr SpinC. Ue Man (1908) has probably included the tcrniinal claw in his measurement of the length ; if SO, his ratio of length to breadth of dactylus woultl be greater than those in Ttble 11. by 0.40-0.70 approximately. The length of the cheliped is always measured t o tho distal extremity of the immovable finger, which is somewhat shorter than tho movable onc. It is possible, tliercfore, that the ratio given for finger-length to palm- lengtli are somewhat smaller than those given by do Man (1908).

PRAWN8 OF THE SPECIES CARIDINA NILOTICA. 41

4.80 to 5.20 for permpod 5 (de Mans figures a re 4.20 to 4.80 and 5.00 t o 6.00, see footnote).

Specimens from t h e open waters of Lake AlbertJ, taken at depths of 10-40 metres, are rather similar to the preceding form, b a t the palm id still shorter i n both chelipeds (text-fig. 9) ; the ova a re considerably smaller than in C.nilotica var. typica, but of the wme size as i n specimens from the Victoria Nyanza. The two preceding forms (Table II., A, 4 and 5 ) are regarded as lacustrine modifications of G. wilotica.

The material from Lake Kwania has, RS i n C. nilotica var. typica, a relatively long palm i n both chelipeds, but the ratio of carpus-length to brwtltli is higher, and that of clieln-length t o carpus-length lower in tlie second peiaopotl. The dactyli of the walking-limbs are also somewlint longer than in t h e typical form.

Text-figure 9.

First pcrzcopod of: a, C . iziloticn var. typica from the Lower Nile ; b, of lacustrine form from the Victoria Nyanza. X 35.

Mr. Grahams material from t h e Victoria Nyanza is of two types. The specimens taken close t o t h e shore agree with C. lzilotica viil-. typica save tha t the ova are somewhat smaller ; all previous aollecfions from thi.; TAake in t h e British Museum are also of this form *. The specimens iiihahiting t h e open waters of the lake have a short palm t o each cheliped and long slender dactyli on tlie succeeding persopods. The number of dactylar spines is higher and the ova are smaller than in the shore form, while the ratio of propodus-length t o dactylus-length for peraopods 3 R.nd 5 is lower. In six of the nine specinleiis rneasuretl tlie ratio of cnrpus-length t o breadth is higher i n the first c,heliped. This short-palmed form is ra.tlier similar t o those from Rutiaba. a.nd from t h e open waters of Lake Albert i, but the dactyli are rnuch more slender and t h e pa.lm is not quite so short as i n the latter.

0 The specimens lent by the Paris Museum are also similar to the shore form. t The lacustrine specimens from Butiaba and the open waters of Lake Albert arc all apparently

immature, and the maximum number of dactylar spines is, therefore, unknown.

TA

BL

E 11

.

Size

of

Ova

in

mm

. L

ocal

ity.

D

iffe

renc

es f

rom

C n

ilotic

a va

r. t

ypic

a, fr

om E

gypt

, in

I-v.

a. 2

.14

-2.4

7 I a

. 5.

05 -

5.79

x.

4.41

- 4

.86

C.

1.17

-1.

30

I C.

0*77

'-0'81

Z.

9 -1

1 I

-

I---- a.

2.0

0 -2

.16

1 a.

4.32

-4.

33

O.

3-43

- 4

.09

b. 1.

09 -

1.17

(3).

3. B

uhuk

a, L

ake

Alb

ert

(3)

I b.

1-12

-1.2

3 y. 3

.50

- 3.

80

c.

1.21

-1.

43

I c. 0.

85 1

0 94

z.

6 -1

2

1 a. 1

.90

-2.2

7 1 a.

3.0

0 -3

.65

1 b.

1.50

-2'

36

1 b. 1.81 -

2'45

4,

But

iaba

. Lak

e A

lber

t (5

).

C.

1.30

-1'

58%

C

. 0.

95 -

1'20

" ___________-_

______--

__--

___--

{I

2.

2.43

- 3

.24

y.

4.20

- 4

.75

I.

8 -1

0

a. 3

00an

cl3'

25

1 b. 2.

57 ,,

3.18

5.

Lak

e A

lber

t, op

en

I c. 1

.18

,, 1.

19

x. 2

.67a

nd2.

70

y. 4

.67

,, 5.

00

e. 8

,, 9

a. 2

.05

-2.4

9 I a.

4.9

3 -5

.67

z.

4.10

- 5.

00

b. 1

.00

-1.3

0% 1 b

. 1.

06 -

1.28

C.

1'

10"-

1.28

I C.

0.

75t-

0.82

2.

8 -1

0 y.

2.70

- 3

'54

i 7.

Vic

tori

a N

yanz

a (1

0).

1 V

ario

us c

olle

ctio

ns.

r 6.

Lak

e X

wan

ia (4).

4 ( ~

_-_

__

__

-_

__

_

I

V.

5th

Pern

opod

.

a. 2

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0*

i a. 5

.001

-6.8

7 0

. 3.

93 -

4'2

3 b.

1.

00 -

1.22

I b

. 1.

04 -

1.19

y.

3.

901-

4.

40

C.

1'15

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37

C.

0.71

-0'

78

Z.

8 -1

0 _

__

_-

~-

F.

3.08

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75

a. 3.

50 -

4.5

0 z.

32

-52

c.

3'23

- 3

.59

z. 45

-5

0

-_.-

y.

4.65

- 5

.00

1. 0

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0.60

b.

0.32

-0'3

6

--- As

abo

ve.

8.

3.11

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y.

4.18

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.36

5.

36

-40

__---

B.

2.20

-

2.53

1/

. 5.

00 -

5.8

9 Z.

33

-4

0

x. 2.

09 a

nd2.

17

y. 5

.80

,, 5.

80

8. 33

,, 3

6

2.

3.35

- 3

.46

y.

3.25

5-

4.80

2

. 21

-4

2

2.

3.20

- 3

.90'

y.

3.46

'- 4.

50

Z. 38

-6

0

x.

3.00

'- 3.

60 -

y.

3.80

- 4

.00

e.36

-3

9

L. 0%

-0.

78

b. 0

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0.52

b. 0

3-0

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VY.

1. 0

.62-

0'66

1

6. 0

.38

-0'4

0 i

" 0

'54-

0'57

I}

IIb

; 11

1s ; VB.

b. 0

.31

(Im

mat

ure)

. Ib

; II

C : I

IIy

; vy.

Spec

imen

s all

un

der 2

1.5

mm

. ii:;

IIIy

; Vy (

50 %

).

a. 2

.33

-3.5

0 b.

1.60

-2.

14

c. 1.

08+-

1.35

9.

Vic

tori

a N

yane

a,

wat

ers

(9).

E. 4.

40 -

5.1

0 y.

3

27

-. 3.84

I.

8 -10

z. 4.

24 -

4.7

2 y.

3.

05 -

3.5

0 I.

9 -1

0

a. 2

.10

-2.3

7 10

. L

ake

Tan

gany

ika,

aff

luen

ts

b.

-l.18

{I C. 1

.18

-1.3

9 of

(3)

.

x. 3.

44 -

3.5

7 y.

4.

37 -

4.5

0 Z.

52

-5

4

x.

3.00'-

3

33

y.

4

38

- 476'

Z.

35

-50

a. 2

.561

-2.7

0 b.

1.22

-1.

50'

Chr

isty

and C

unni

ngto

n C

oll.

11.

Lak

e N

yass

a (4

).

Z.

49

6 - 5

.00

y.

2.90

I. 10

-13

a. 2

.29

-2.5

0 b.

1.

03 -

1.26

C.

1.

14 -

1.27

12

. L

ake

Nga

mi

(3).

--_--

O.

3625

- 4.

00

y.

3.26

*-

4.10

e. 41

-62

a. 1

.95

-220

b.

0.93

-1.

17

G.

1.17

-1.

30

Nat

al.

13.

Riv

er U

mge

ni (

3).

x.

5-33

- 5

.66

y.

2.37

"-

3.33

Z.

10

-11

a.

4.00

- 4.37

y.

3.07

- 3

.66

0.

8 -[11]

a. 1

.98

-2.1

2 14

. S

trea

m n

ear

Gre

ytow

n (3

).

C.

1.12

-1'

24

z.

3'55

5-

4.41

y.

3.

75 -

4.1

7 Z.

56

-7

8

o.

2.85

- 3

.00

y.

4.54

- 5

.00

z. 34

-4

4 [z

. -6

0 in

G

raha

m's

spe

ci-

men

s].

B. C

arid

ina

afri

cana

.

15.

Egy

pt (

3).

No

ova,

bu

t spe

cim

ens

mat

ure.

No

ova,

a.

2.0

0 -2

.40

b.

1.30

-1.

50

C. 1.

33 -

1.50

1110;

vx

.

vz.

IIb

-_------

3

a. 3

.50

-6.2

4"

b. 1.40 -

2.20

C.

096t

-1.1

5

a. 4

.86

-5'4

0 b.

1.0

0 -1

.25

c. 0.

75 -

0.84:

a. 5

.435

-6.8

7 b.

1.17

-1'

22

c.

0.69

-Of445

-

~-

a. 3

.07

-3'3

65

b. 1.

21 -

1.2'4

. C.

0.75

*-0%

0

a. 4

.50

-5.0

0 b.

1.15

-1.

19

C. 0.

76 -

0.78

a. 4

.22

4.7

7

b. 1,

301-

1.54

c.

0.

70*-

0%2

a. 4

.50

-5'2

6 b.

1.3

0 -1

'53

c.

0.80

-0.

89

a=le

ngth

+br

eadt

h of

car

pus.

b=

leng

th o

f fi

nger

sfle

ngth

of

pal

m.

c=le

ngth

of

chel

afle

ngth

of

carp

us.

xzl

eng

th of

pro

podu

s fle

ngth

of

dact

ylus

. y=

leng

th f

bre

adth

of

dact

ylus

. z

=nu

mbe

r of

dac

tyla

r sp

ines

, ter

min

al c

law

incl

uded

.

E. 2.

63 -

4'1

6x

X.

2'04

- 3

.205

y.

4'

37 -

7.0

0 y.

6.00 -

7.

25

Z. 5

-15

B. 11

-7

2

Z.

43

3 - 4.

60

Z.

32

6 - 3.

56

y.

3.50

- 3

.75

y.

4.50

5-

5.00

Z.

9

-10 I---

8.

47

-51

2. 0

.50-

0.52

b.

0.31

-0.3

2

1. 0.

68-0

.73

b. 0

.43

-0.4

7

1. 0

-65-

0.67

(Sm

alle

r ov

a .n

Cun

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44 DR. ISABELLA UORDOh : AFRICAN FRESHWATER

From a swvey of the material fronr Lake Victoria. to the Lower Nile itb seems that C. nilotica var. typiccc occurs throughout the whole area with but little

Text-figure 10.

Second peraopod of the same two specimens as in text-fig. 9. X 35.

Text-figure 11.

Dactylus of the third perzopod (a and hits in text-fig. 9). A 80.

variation. I n the lakes the typical form is confined, as a rule, t o the shore area, the oya are smaller, and the type of telson represented in text-fig. 2 is more

PRAWNS OF THE SPECIES CARIDINA NILOTICA. 45

numerous. Along with t h e typical variety another distinct slender-limbed lacustrine rariety (or varieties) occurs in Lakes Victoria and Albert. Yhe differences between t h e lacustrine form of Lzke Victoria and C. nilotica var. t?ypica are clearly demonstrated in text-figs. 9-12. It may be ttiat C. iailotica tends to give rise to a locnl lacustrine form in all t h e deeper African lakes into wliicli i t enters. From Table 11. i t is apparent tha t the specimens from different localities may differ slightly from each other. For example, G. iailotica var. typicu from the Victoria Nile above Mnretiisori Falls has, on t h e whole, a higher ratio of length to brendth of carpus than the specimens from Buhuka, Lake Albert, The same is true of the ratio length of propodos t o length of dactylus, with a little overlapping in the case of t h e fifth pemopod. Moreover, t h e ratio of length of finger t o length of palm is higher in the first peraopod, as also i5 t h a t of length to breadth of dactylus in the fifth peraeopod. Although all the 18 specimen8 from Egypt have

Text-figure 12.

b. a

Dactylus of the fifth poraopod from tho saiiic specimcns as in tcxt-fig. 11. X80.

heen treatetl as one group, certain ratios tent1 t o he rntlier higher in speciiiiens fl,oin certain loca.lities tliaii in t l i ose fi,oiii other localities, e . q., specimens froni (;iz:i have, as :I, rule, a liiglier ratio of Ir:ngt,li to brerltltli of c:irpus and of l e n ~ t l i of propodus to length of tl:i.ctylris tli:in 1i:tve speciiiiens from Por t Saitl.

Tile survey of C. niloticc~ from other p u t s of Africa is of necessity incoiiiplet;., owizlg to the small niiiriher of speciinens frolii localities in N:tt:rI ant1 tlie nhseiice of material from t h e open waters of Tiikes Nynssn m t i Nganii. Specimens fronl t,lie a fAue~~ts of L d i e TaiipIlyika n~ .en l~nos t it1eiitic:ll wit,li C. niloticcc var. t?ypicn hotli ns regnrcls permopod i.iitios arid size of ov:~. *. It is of interest to f ir i t l tile t-ypicnl form occurring in tlie vicinity of tliis fresliwnter lake, wliicli Ii:ts no connection whatever witli tlie Nile systcnl.

t The rostrum is somewhat different, however ; see Table 111.

46

Locality.

A. Caridina nilotica. 1. var. bypica from Egypt.

~~~

Worthington Collection. 2. Buhuka, Lake Albert.

-~__I__----

3. Butiaba, Lake Albert. St. 146.

~~ ~

4. Butiaba, Lake Albert. St. 136.

5. Lake Albert, open waters.

I--..--_-..---- 1 6. Lake Kwania. 1 7. Victoria Nyanza (Cunnington). j j I waters.

I-------------- 8. Victoria Nyanza (Graham), shore.

I-----------

9. Victoria Nyanza (Graham), open

i 10. Victoria Nyanza (Bouvier det.), Paris Mus.

11. Lake Tanganyika, affluents of.

j 14. Natal : River Umgeni.

15. Natal : stream near Greytown. i I I 16. Natal. C. nilotica var. nntalensks 1 (Paris Mas.).

, B. Caridina ufrtcnnn. j Nyansa. Egypt and stream near the Victoria

~~~~~~~

Rostra1 formula. (Typical examples.)

~

18+1 19+1 22+1 21+1 1pj- ; 1 6 ; 23 ; --___.________.--

15+1+1 18+1 15+1+1 16+2 14 2 0 1 8 16 ___..__.-

----- I ? 16 PI+] 20+1 21 1 5 10+1 13 16 5

124-1 14+1 1 7 + ? 18

- . - . _ _ . _ _ . --- -__-

I T ; fi

20+1 20+2 19+1 18+1+1 , 2 s ~ ; 23- . - ~ - - . -

20 24 20

16+2 18+1+1 1 9 T 1 20+1 14 ; 17.-. __ . _- 15+1 13

2 l t l 18+1 24+2 23+1 ; r ; 24; 2r

__ . _ _ _ ~ . 13 18

22+1 21+1, T4L2 , 2 2 1 15 13 13 16 __ . - - ~

19+2 . 16+1 . 18+1 . 18+1 18+1 __ __ g , 7 * 7 3 5-+3 i -8

19+1 1 7 1G+1 16+1 16+1 19 18 18 25 26

~. - . . - .

TAI

_ -

m. 47

2. Dorsal group minus ventral

group of rostra1 spines.

1. Proportion of

dorsal surface of rostrum unarmed

3. Ratio of

,ostrum-length to carapace-length.

Differences from C. nikjtiea var. t y p ~ e a from Egypt.

027-0.48 * - 1 t o + 9 1.19 - 1.38: 1

0.42-0.48 + 3 to + l U 1.32 - 1.38: 1 _____-

1.70 - 1.75: 1 0.51 -0.56

- ~ ~ - - 0.36 -0.52

1. Greater part of dorsal surface unarmed. 2 . Ventral spines tend to exceed dorsal group. 3. Rostrum longer in proportion to carapace.

+ l t o - 3

1. Greater part of d. s. unarmed in largest specimens. 2. See text, p. 48. 3. Longer rostrum in largest specimens.

1. Greater part of d. s. unarmed in oldest specimens 2. See text. 3. Rostrum longer in oldest specimens.

-____ _____-- i 4- 2 t o + 8 1.20 - 1.50: 1 + O t o + 2 1.43 - 1.73: 1 0.45-0.50

0.40-0.54 $1.33 - 1'71: 1 1. Greater part of d. 8 . unarmed. 2. Ventral spines generally exceed dorsal group.

13. Rostrum longer. - _ _ _ _ _ ~ - . _ c _ ~

"f 1 to - 6

_ _ ~ - 0.38-0.44 1.12 - 1.36: 1 + l t o + 7

0 4 - 0 . 4 3

0.45-0.52

+ 2 t o + 5 1.16 - 1.33: 1

1. Greater part of d. s. unarmed. 2. Ventral spines tend to exceed dorsal group. 1 3 . - Rostrum longer.

- _ _ ~ ~ _ _ _ _ ~ _ _ - _ _ -

*+ 1 to - 4 1.31 - 1.70: 1

0.36-0.38 - 2 t o + 4 1.10 - 1.31 : 1

[ 1. Greater part of d. s. unarmed. ' 2. Ventral spines often exceed dorsal group. 1 3. Rostrum sometimes longer.

2 . More spines in dorsal group.

0.46-0.50 + 4 t o 3 1.10 - 1.43: 1

0.33 0.37

0.30-0.40

t (i to +12 1.20 - 1.37: 1

t 3 t o + 8 1.00 - 1 .17: 1 3. Shorter rostrum.

+10 to +13 0.91 - 1.14: 1 f 2 . Very few spines ventrally.

3. Shorter rostrum. ~ _ . _ ~ _ - - _ _ - _ _ -

r 2. Ventral spines cnerally exceed dorsal group. 3. Shorter rostrum.

0'21-0.33

0.83 - 1.00: 1 0'43-0.47 - 0 to -10

1.21 and I .3C : 1 0.35 and 0.50

[ 1. Shorter portion unarmed dorsally. 13. Rostrum always shorter than carapace.

2. Few spines in ventral group. 0.78 -- 0.88: 1 + 7 to +I8

* Unusual.

48 DR. ISABELLA GORDON : AFRICAK FRESHWATER

The rest of t h e material of C. n i l o t i c a belongs t o the group with apex of telson characteristically as in text-fig. 3 (see Table I.). The specimens from Lake Nymsa, collected p i i t ly by Christy partly by Cunnington (Calman, 1906, pp. 189-191), are also near G. nilotica var. typicffi j t h e ratio of carpus-length t o breadth is greater i n both clieliptds, while in the stcoii(t cheliped two of the four specimens ineasuretl li:itl :I sriialler ratio of lerigtli of chela to length of carpus. This local race is nearer t o vnr. typica t h a n to var. grtcciZi1)es de Man, although Dr. Calman (19061 has tlescritird these specimens and material from the Victoiia Njanza under t h e la t ter va i iek l n:ime. The ova in nr. Cunnington's specinieiis are smallei than i n mi.. typiccc, measuring only 0.52-0.56 mrii. in length, 0.32-0.37 inni. in breadth.

The specimens fixmi Lake Nganii appi oncli C. niloticffi var. typica closely, but have iL more 4entler GWEJUS t o the secoild clieliped, a moie elender dactylus t o the fifth perzeopot?, arid larger ova.

The two forms frorn Natal both differ considerably from tlic typical Egyptian material, as Table 11. shows. Moreover, they diEw sliqbtly from each other, t h e ratio of length of finger t o length of palm in both chelipeds and of len6th of propodus to leiigth of dactylas in the third perzopod being smaller in t h e specimens froni River Umgeni. The rostra1 formula is also rnarlretlly different in tlie two (see Table TJJ.), altltoiigh in both the rostrum is shorter than i n C. nilotica var. typica.

Cayidina qfvicana from Egypt diffeis from C. iiilotica var. typica i n h iv ing ( 1 ) ~ shorter palm to e Ich che l ipd , ( 2 ) a somewhat longer and more sleridrr dactylus on the fifth perzeopotl, a n d (3) a smaller ratio of length of propodns to length of dactylus for t h e latter. The figures in hriiclrets give t h e number of dactylar spines in an adult specimeii from Bukoba River.

PRAWNS O F THE SPECIES CARIDINA NILOTICA. 49

1.n specinieiis from the d u e n t s of LRke Taiiginyilia. the rostrum approximates to that of tlie lacostrine forms (see Table I tJ . ) , but is neither so slender nor so curved :IS in the I:it,ter. In other respects tliese specimens a re very near to the Egyptian typical sariety.

'!'he rostrum i r k forms froni Lake Nyaas;~ is siiiii\ar to t h a t of c. szzboticcc var. typica, biit the tlorsnl spines are soinew1i:~t more iinrtici'oiis. I n specinlens from L-ike Ngaini tlre rostriiiri is of the s :me type, bu t sliorter than tha t of the typical form.

The Natal specimens are of nrnch 1a.rger size tlinri tlre other Africa.11 prawns, and the rostrnm is unusually short,, Ijut the two 1oc:tl forms show a distinct difference iri tlre rostra1 forniulr>.; that of the Kiver Uingerri nia.teria1 is remxr1txl)le for the i~elativvly nrn:ill number of t h e ventral spines, t,lrat of t h e Greytown nixteri:rl

Text-figure 13.

a

b

Kostrnm of ! a, C. ri,fiicntm var. wgyptinen froin BukubaRix-er ; 74 C. ~ ~ i l o t i c n var. fypicn from Egypt: and c . C. i d o f i e n . laenstrine form from I.alic Victoria. (Specimens from which figs. n a n d b mc re obtained YIWW of e(liia1 length, that from nhicli fig. c was obtained was mther smaller.) x 14.

has the ventral spines equal to or greatly outnumbering the tlorsnl group. Apparently neither form agrees with c. ndoticcc var. irataleizsis (Paris Museum material).

The rostrum of 6'. c~fricancc is always shorter t , h n t h e carapiee, iins n very small proportion of the dorsal surface unarmed, and relatively few ?.pines on the ventral surface. I n the la t ter character it shows a slight reseniblance to the form from Rive Umgeni.

CONCLUSION.

All over East Africa there is a vast assemblage of slight local deviations from the form which, from its occiirrerice in the type-locality, nmiely, the Lower Nile, has most r ight t o be called C. szilotica var. t?jpicrc. Whether these local deviations

PROC. ZOOL. SoC.-l930, No IT 4

50 AFRICAN FRESHWATER PRAWNS OF THE SPECIES CARIIJINA NILOTICA.

merit special varietal names need not be discussed here. I n each of the two large lakes, Lake Albert and Lnke Victoria, t8here OCCUI*S, in addition to C. nilotica var. typical a form (or forms) apart which may be regarcled as a lacustrine modification.

LIST OF \;YORKS REFERRED TO.

BOUVIER, E. L. (1925.) CALMAN, W. T. (1906.)

EncyclopCdie Entomologiqrro. -1V. Atyides, pp. 1-307. Macrurous Crustmea of the Third Tanganyika Expedition.

Paris. P. Z. S.

1906, vol. i. pp. 187-206. pls. xi.-xiv. - (1928.) . On Prawns of the Family Atyidcc from Tauganyika. P. 2. S. 1928, pt. 3,

pp. 737-741. GURNEY, R. (1927.)

KEMP, S. (1918.)

DE MAN, J. G. (1908.)

Report on the Larv;e of Crustacee Decapoda. Trans. 2001. SOC. pi. 2,

Mem. Asiatic Soc. Bengal, vol. vi.

.On Cal-idiran nilotica Roux and i t s Varieties. Rec. Ind. Mus. vol. ii

1927, pp. 231-286.

pt. v. pp. 217-297.

pt. iii. no. 28, pp. 255-283, pl. xx.

Crustacca Decapoda and Stomstopoda.