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Fauna of the Chilka Lake : Crustacea Decapoda. 



267 



P. malcolmsoni, ? . 



Rostrum longer, reaching to or beyond apex of 

 antennal scale; proximal margin of upper 

 border markedly convex, apex a little upturned. 

 Dorsal teeth aggregated on proximal part; 

 teeth on distal part few, either confined to 

 apex or very widely separated. Three dorsal 

 teeth on carapace. 



Inner and outer margins of antennal scale sub- 

 parallel. 



Chela of first peraeopods with fingers decidedly 

 shorter than palm. Palm with large patch of 

 coarse setae on its infero-internal aspect. Fin- 

 gers gape at base when claw is closed. 



Second peraeopods with fine spinules arranged in 

 longitudinal rows. Dactylus in very old fe- 

 males densely covered with hairs. Carpus 

 shorter than palm + half the length of fingers. 



P. rudis, 9 . 



Rostrum shorter, reaching at most to apex of 

 antennal scale. Upper margin straight or very 

 slightly convex, apex not upturned. Dorsal 

 teeth almost evenly spaced throughout length 

 of rostrum. Two dorsal teeth on carapace. 



Inner and outer margins of antennal scale ante- 

 riorly convergent. 



Chela of first peraeopods with fingers equal in 

 length to palm. Palm with small patch of 

 coarse setae on its infero-internal aspect. Fin- 

 gers do not gape at base when claw is closed. 



Second peraeopods practically glabrous. Carpus 

 longer than palm + half the length of fingers. 



A series of very much smaller specimens found at Satpara in March 1914 may 

 also belong to this species, though they differ markedly from the larger individuals 

 noticed above. The series comprise several ovigerous females and a few males in 

 which the appendix masculina is to all appearances fully formed ; the largest speci- 

 men, an egg-bearing female, is 58-5 mm. in total length. The great difference in size 

 between this individual and those found at Barkul is not, of itself, sufficient to dis- 

 prove the specific identity of the two series of specimens. Henderson and Matthai 

 have pointed out that species of Palaemon may be sexually mature when extremely 

 small in size and that males may possess well-developed testes containing free sper- 

 matozoa long before their chelipedes have reached the dimensions characteristic of 

 large members of their sex. There is reason to believe that a precocious sexual 

 development of this nature occurs in the case of Palaemon rudis in the Chilka Lake 

 (vide infra). 



In the specimens from Satpara the rostrum in both sexes is much more strongly 

 upturned distally and the crest on the dorsal margin is less elevated than in 

 the large females found at Barkul. The teeth are also rather larger proportion- 

 ately and those on the upper margin are more evenly distributed, though those 

 situated behind the one or two placed at the apex are in most cases separated by 

 distinctly wider intervals than those near the rostral base. There are 11 or 12 dorsal 

 and 5 or 6 ventral teeth ; of the former three are situated on the carapace behind the 

 level of the orbit. 



The antennal scale is distinctly narrowed towards its distal end, thus differring 

 from that of the larger specimens ; in the chela of the first peraeopods there is a closer 

 resemblance, but the fingers do not gape at the base when the claw is closed. 



The length of the second peraeopods, in both males and females, is only about 

 70 % of the total length and the proportionate length of the ischium, merus, carpus. 



