I9I5-] 



Fauna of the Chilka Lake ; Crustacea Decapoda. 



281 



individuals, by the length of the chela and half the carpus. In the male they are 

 decidedly longer proportionately, reaching beyond the scale by the chela and two- 

 thirds the length of the carpus. The limbs of five separate specimens yield the 

 following measurements l (in mm.) : — 



Sex. 





Second y 



eraeopod : 



length of 







Ischium. 



Merus. 



Carpus. 



Palm. 



Dactylus. 



c? 



2-2 



3-2 



32 



20 



2-1 



d 1 



20 



2-9 



3-0 



i-q 



2-1 



2 



2'I 



32 



3'3 



2-4 



i-8 



2 



2 - 



27 



27 



22 



1-5 



? 



2"0 



2-6 



27 



2'I 



i-6 



It will be seen that the merus and carpus are about equal in length and that the 

 latter segment is considerably longer in the male than in the female and in the former 

 sex is conspicuously longer than the palm. The fingers in the male are a little longer 

 than the palm, while in the female they may be less than three-quarters its length. 

 There is a spine at the distal end of the merus, situated inferiorly, and one at the 

 distal end of the carpus, placed internally. There are a few very small teeth, some- 

 times as many as six, on the inner half of the fixed finger and others, still more 

 minute, similarly placed on the dactylus. 



The third, fourth and fifth pairs of peraeopods reach to, or a little beyond, the 

 apex of the antennal scale. In those of the fifth pair (text-fig. 27g) the propodus is 

 a trifle longer than the merus, about twice the length of the carpus and nearly three 

 times the length of the dactylus. The propodus bears setae at its distal end and five 

 or six spinules on the inner border; the dactylus is slender, slightly curved and with 

 a few setae in the middle of its outer margin. 



The only gills which are well developed are the five pleurobranchs. The pleuro- 

 branch found in Palaemon at the base of the third maxillipedes is absent, while the 

 arthrobranch of the same segment is represented only by a few lamellae. There is, 

 apparently, no trace of a podobranch on the second maxillipede. 



There is a marked difference between the sexes in the form of the pleopods. In 

 the male the protopodite is about equal in length to the exopod, whereas in the 

 female it is proportionately half as long again. The greater length of the segment in 

 the latter sex is correlated with the greater depth of the abdominal pleura; it is 

 doubtless a provision to enable the pleopods- to have free play when the female is 

 heavily laden with eggs. 



The abdominal somites are smooth ; the sixth is little more than half the length 



1 These measurements are taken from specimens found in the Chilka Lake. In ovigerous females 

 from the neighbourhood of Madras, which are of considerably larger dimensions, and in a few examples 

 from the Chilka lake (text-fig. 27e) the palm is a little longer proportionately, about equal in length 

 with the carpus and merus. In a male from Madras the proportional lengths of the segments of 

 the second leg are much as in the Chilka specimens, but the limb is longer, reaching beyond the apex 

 of the scale by the chela and the whole length of the carpus. 



