3o8 



Memoirs of the Indian Museum. 



[Vol. V, 





Calcutta 

 (Garia). 



Chilka 

 Lake. 



Madras 



(Villy- 



vakkam). 



Tuticorin. 



Colombo. 



No. of specimens examined 



Dorsal teeth of rostrum, basal crest only . . 



Ventral teeth of rostrum 



Average no. of dorsal teeth 



Average no. of ventral teeth 



Length of eggs (mm.) 



149 



15-30 



11 -22 



227 



147 



•41— -48 



100 



14—25 



6 — 19 



19-1 



12-0 

 •42 — -48 



200 



14—27 



9—20 



197 



136 



•42— -49 



34 



15 23 



11 — 19 



19-0 



156 



•47— '475 



91 



13—23 



8—18 



16-8 



13-2 



■43 



In his work on the varieties of C. nilotica, de Man notes that var. bengalensis is 

 very closely related to var. gracilipes, de Man, a form found in Celebes and Saleyer. 

 From this race the Indian form is separated by the greater number of teeth on the 

 upper edge of the rostrum and by the larger size of the eggs ; but it seems probable 

 that a distinction based on these grounds is untenable. The number of dorsal teeth 

 in Indian specimens ranges from 13 to 30 and in var. gracilipes from 12 to 20. In the 

 former the average number varies from 168 in the case of Ceylon specimens to 227 

 in the case of individuals from the vicinity of Calcutta, while in the latter, according 

 to the results of de Man's examination of twenty-five specimens 1 , the average 

 number is about 15-8. The eggs vary in length from -33 to -40 mm. in var. gracilipes 

 and from "41 to '49 in var. bengalensis. 



Should it prove that no other distinctions are available, the name gracilipes 

 must be used for the Indian form. 



In the Chilka Lake Caridina nilotica was found only in Rambha Bay and in the 

 outer channel; but in both these localities it was abundant. In Rambha Bay it was 

 plentiful among weed near the margin of the lake and was also found near the rocks 

 at the foot of Ganta Sila. Ovigerous females were taken both in February in water 

 of sp. gr. 1 -on and in September in water of sp. gr. 1*006. 



In the outer channel it was obtained in February at Satpara and near Mahosa in 

 water as salt as that of the Bay of Bengal near the lake (sp. gr. 1-0265), but no 

 females bearing eggs were to be found. In September when the water was fresh and 

 stood at a level some 5 ft. higher than in February, the species was common in the 

 same localités, living among the roots of screw-pines, and was also found in sub- 

 merged grass on islands near Manikpatna. At this time of the year numerous egg- 

 laden females were obtained. Our observations seem to indicate that very saline 

 water inhibits reproduction. 



The absence of C. nilotica from the vicinity of Barkul and from other places in 

 the main area where weed is plentiful and the conditions apparently favourable is 

 perhaps to be explained by the enormous abundance of C. propinqua in these locali- 

 ties. This prolific species has perhaps ousted C. nilotica from situations in which it 

 would otherwise have occurred. 



1 de Man, in Weber's Zool. Ergeht. Niederlande Ost-Ind., II, p. 394 (1892). 



