I40 



Records of the Indian Museum. [Vol. XXII, 



Indian Museum collection. Some of these shells are much larger 

 in size than Prime's type-specimen. 



Measurements (in millimetres). 



Specimen A is from Cochin-China, B from Cambodia, C and 

 D from the Nicobars while E and F are single valves only from 

 Rangoon, Burma. 



Distribution. — The species was hitherto known from Siam 

 only but from the series of specimens in the Indian Museum 

 collection it appears to have a very wide range from Cochin- 

 China, Cambodia to Burma and the Nicobar Islands. 



Cyrcna itnpressa, Deshayes. 



Plate XX, figs. 6,7. 



1854. Cyrem impyessa, Deshayes, Proc. Zool- Soc London, p. 18. 

 1854. Cyrena impressa, Deshayes, Cat. Brit. Miis. Cojichifera II, p. 



249. 

 186,^. Cyrena exirnta (in part). Prime, Cat Corbiculidae, p 6. 

 i86g. Cyrena e.ximia(\n part), Prime, Amer. Joiirn. Conch. V. p. 144. 

 1879. Cyrena cev/o7zica(\n part), Clessin, Cycladeen in Martini-Chemn 



Conch. -Cab., p. 103, pi. xviii, figs, i, 2. 

 1879. Cyrena eximia (in part) id . ib.. p. 239. 

 1897. Cyrena impressa, von Marlens, S/iss und Brackw. Moll, in 



Weber's Zool. Ergeb Nieder. Ost.-Ind. IV. p. 93. 

 1915. Cyrena impressa, Preston, Faun. Brit. Ind. Fresii-w.-Moll. pp. 



202 — 204, figs. 25, 26. 



Prime and Clessin after him considered C. impressa as a sy- 

 nonym of C. eximia, Dunker, but von Martens has shown that 

 the two species are quite distinct and even belong to different 

 groups in his scheme of clas.sification cited already. Deshayes' 

 description is fairly detailed and accurate, while von Martens 

 added a few further notes on the species. Recently Preston has 

 published good figures of the tj'pe-shell. The following distin- 

 guishing characters of C. impressa may, however, be noted. The 

 anterior margin is straight or nearly so, while the posterior mar- 

 gin is only slightly convex in its upper or pro.Kiinal half and then 

 sharply turns down at an obtuse angle, this distal half is nearly 

 straight and the margin here may be described as subtruncate, 

 the ventral border is regularly but not greatly curved and the 

 umbones are not very prominent. 



Distribution. — According to Deshayes C. impressa is found in 

 the Philippines, Java and Australia. Preston, on the basis of 

 specimens in the British Museum, included Ceylon in the ranee of 



