300 Memoirs of the Indian Museum. [Voi,. V, 



base of the hoods as a thin well-marked crest (not flattened above) and is rendered 

 the more conspicuous by the comparatively deep depressions which exist on either 

 side of it. The dorsal edge, which is, as a rule, a little concave, is concealed in lateral 

 view by the rather elevated eye-hoods. 



The dactylus of the smaller chela of the male is subspatulate in form, " Balaeni- 

 ceps "-shaped; in the female the dactylus of this chela is slender. In both limbs and 

 in both sexes there is a sharp spinale at the distal end of the infero- internal margin 

 of the merus, while there is no tooth on either side of the insertion of the dactylus. 



In the large chela the depressed area on the supero-internal face is triangular in 

 shape and the lobes on the upper and lower margins of the palm are distally rounded 

 (not acutely produced). The small chela of the male is scarcely, if at all, more than 

 three and a half times as long as wide and the palm is distinctly notched, both dor- 

 sally and ventrally, behind the fingers. 



The merus of the third legs is without teeth and is rather less than five times as 

 long as wide. The dactylus of the last three pairs of legs is simple. 



The specimens which possess these characters were found among clumps of 

 oysters in the. outer channel of the lake and agree very closely with de Man's 

 detailed description (op. cit., 1902). When the antennule is dissected out, the second 

 peduncular segment proves in reality to be but little longer than the first, though, if 

 the measurements be taken along the inner edge, the former is, as in de Man's 

 account, about one and a half times the length of the latter. In the large chela the 

 total length is from 21 to 23 times the greatest width, the claw being therefore 

 rather broader than in the specimens examined by de Man in which the same propor- 

 tion varies from about 2 3 to 2 "45. 



Other examples found under rocks at the south end of the main area of the lake 

 differ rather notably from those obtained in the outer channel, but must, I believe, 

 be referred to the same species. In all these specimens the rostrum is less sharply 

 carinate than in the others and the grooves on either side of it are broader and shal- 

 lower. The large chela also is narrower — a difference readily noticed without mea- 

 surement— the length being from 24 to 2-48 times the greatest breadth. In other 

 respects these individuals agree with those from the outer channel. 



Dr. de Man, when examining the 'Siboga' material of this species, notes that 

 two specimens from a single locality differ notably from the remainder in having 

 stouter limbs, and it is probable that phases showing more or less distinct minor 

 characteristics, presumably adaptational, are to be found in different regions. The 

 occurrence of two such phases in the Chilka Lake is of no little interest, owing to the 

 close proximity of the localities in which they were found and to the wide differences 

 in environment. 



The form obtained in the outer channel lives among clumps of oysters, practi- 

 cally always submerged; the water, during some nine months of the year, is as salt 

 as that of the Bay of Bengal outside the lake (sp. gr. 10265), while for the other 

 three it is almost entirely fresh. The form occurring at the south end of the main 

 area is subjected to much less violent changes in salinity and lives under stones and 



