696 Memoirs of the Indian Museum. [Voiv. V, 



permanent inhabitant of the thickets of Potamogeton pectinatus that occur all over 

 the Chilka Lake. What I take to be this prawn was common in these thickets in Ram- 

 bha Bay in the rainy season of 1919, and I have no reason to think that it is less so 

 now. 



The two species of Atyidae found in Rambha Bay in 1914 were Caridina nilotica 

 (Roux) and C. propinqua de Man. Their genus is fluviatile and lacustrine, but both 

 species have been found at more than one locality in brackish as well as fresh water. 

 C. nilotica is represented in India by a race that was called bengalensis by de Man 1 in 

 1908, but Dr. Kemp 2 has recently shown that this race cannot be separated from the 

 same author's var. gracilipes from Celebes and China. Both C. nilotica gracilipes 

 and C. propinqua are still abundant in the Potamogeton thickets of Rambha Bay. 



The family Alpheidae was represented in Rambha Bay in 1914 by two species 

 of Alpheus, namely A. crassimanus Heller and A, paludicola Kemp, the former a 

 marine species, the latter only known from brackish water. In 1919 and in April, 

 1920, A. paludicola was dredged in considerable numbers in the bay with Upogebia 

 heterocheir, which it resembles in habits. A. crassimanus was not obtained, but in 

 1914 this species was less abundant and less liable to be caught in our nets than the 

 other. 



As regards the Penaeidae my observations are very incomplete. This is the 

 more unfortunate as we obtained evidence in 1914 that these prawns did not breed 

 in the lake. Four species were obtained in the bay in 1914, viz. Penaeus carinatus 

 Dana (de Man), P. indicus Milne- Edwards, Peneopsis monoceros (Fabr.) and P. dob- 

 soni Miers. I am not sufficiently well acquainted with these species to distinguish 

 them in the field and can only say that Penaeidae were found in the bay in the cold 

 weather of 1919-20. 



The last Decapod Crustacean to be mentioned is the little Sergestid Lucifer han- 

 seni Nobili, the only completely pelagic species of its class fouud in the Chilka Lake. 

 It was enormously abundant on the surface of Rambha Bay in 1914 on certain 

 occasions but could not always be obtained. Its appearance and disappearance were 

 not correlated with changes in season or salinity. This was observed also in the 

 rainy season of 1919, in December of the same year and in April and June, 1920. 

 There was, however, certainly no diminution in the abundance of the species on 

 the whole. The genus Lucifer is marine, but L. hanseni is known tobe very tolerant 

 of changes in salinity. 



It will be evident from what has been said that there was a considerable reduc- 

 tion in the Crustacean fauna of Rambha Bay in the dry season of 1919-20 as com- 

 pared with that of 1914-15, doubtless in correlation with the reduction of the salinity 

 of water demonstrated by Major Sewell. Some species, moreover, proved more tol- 

 erant than others and while, as might be expected, those of freshwater origin suf- 

 fered less than those belonging to marine families and genera, it is somewhat remark- 



J de Man, Rec. Ind. Mus. II, p. 265, pi. xx, figs. 6, 6a, 6b (1908). 

 % Kemp, Mem. As. Sue. Bengal VI, p. 275 (1918). 



