358 Memoirs of the Indian Museum. [Vox,. V, 



have found it very difficult, with all the types before us, to distribute fresh speci- 

 mens among Preston's three species. 



Anatina granulosa * Preston, 1914, p. 310, "figs. 17, ija. 



The species was described from a specimen long in the Indian Museum and 

 labelled merely l< Chilka Lake." We attribute to it with some doubt a much larger 

 shell found dead on the shore at Ganta Sila in March. 



Anatina barkudaënsis * Preston, 1915, p. 309, figs. 25, 25«. 



Under this name Preston includes the majority of our specimens ; they were 

 found in all parts of the lake except the sandy area of the outer channel. All our 

 living examples were taken in the salt-water season, but the only manner in which we 

 were able to obtain them was by digging on the shore when the water level was low. 



Anatina barkulensis * Preston, 1915, p. 309, figs. 24, 24*7. 



A living specimen was dug up at Ganta Sila in February, and another was 

 dredged near Mahosa in the outer channel in September. The type, obtained at 

 Barkul Point in March, was dead but in a fresh condition. 



NOTE ON VARIATION IN MODIOLA. 



The great abundance of Modiola in the Chilka Lake and the conspicuous nature 

 of the variability exhibited by its species has enabled 11s to prepare notes on this 

 genus of a more elaborate kind than those we have given on other Mollusca. 



Modiola is a genus of cosmopolitan distribution and wide bathymétrie range. 

 M. watsoni is common in the Bay of Bengal at a depth of over 100 fathoms and 

 several forms have been found in inland lakes in eastern Asia. In the estuaries of 

 Indian rivers at least one species is abundant, viz. that referred to below as M. stria- 

 tula, Hanley. 



In the large series of specimens we obtained in the Chilka Lake it is possible to 

 select individual shells corresponding with those referred by Mr. Preston to nine 

 species and one variety ; but, for the reasons stated below, we are convinced that at 

 most only two variable species of different habits are represented. We should men- 

 tion that only a comparatively small proportion of the shells were available at the 

 time that the collection was examined by Mr. Preston. 



Modiola undulata (Dunker). 

 (Plate XV, figs. 1—6: plate XVI, fig. 1.) 



1856. Vulsella undulata, Dunker, Proc. Zool. Soc. Loudon, XXIV, p. 363. 



1858. Modiola undulata, Reeve, Conch. Icon., X, Modiola, pi. v, fig. 18. 



191 1. Modiola chilkaënsis, Preston, Rec. Ind. Mus., VI, p. 41, fig. h. 



1914. Modiola undulata and var. crassicostata, Preston, ibid., X, p. 304. fig. 15. 



1915. Modiola undulata and var. crassicostata, Preston, ibid.. XI, p. 298. 



This species is abundant in the Chilka Lake, occurring at all seasons and in all 

 parts of the lake-system. It is almost invariably attached either to Potamogeton, to 

 filamentous or delicately branching algae or to the ropes of fishing traps ; in other 



