168 Records of the Indian Muscjim. [YoL. XIV, 



In the lakes and rivers of Eastern China many species or races of 

 Vivifcira occur in which the shells are ornamented with spiral ridges 

 of a more or less marked character but are much smaller and thinner 

 than those of Margarya. Figures of these forms will be found in 

 Kobelt's monograph and in Heude's^ account of the molluscs of the 

 Yang-tse. I have recently observed F. lapillorum (Heude), a member 

 of this group, in natural conditions in the Tai-Hu (Great Lake) in the 

 Kiangsu province of China. It lives chiefly on stones near the edge 

 of the lake, in very muddy water and in a district in which limestone 

 is abundant. It is a variable species and apparently not found together 

 with any closely allied form. 



Single species of the genus with similarly but even more strongly 

 sculptured shells have been described from several other eastern lakes 

 and lacustrine districts, e.g., V. grossicosta, von Martens^ from Lake 

 Singkarah in Sumatra, V. ferscidfta, P. & E. Sarasin,^ from Lake 

 Posso in Celebes and Y . oxytrcpis (Benson)* from Manipur in Assam, 

 the basin of a lake which has shrunk in recent ages to small dimensions. 



Moreover, Neumayr's Viviparae from Slavonia, though the most 

 complete series as yet known, are by no means the only forms of a 

 similar nature that have been described from Tertiary beds in Eastern 

 Europe. The first instance of the kind to be discussed was that of 

 certain forms from the island of Cos to which Edward Forbes^ drew 

 attention in 1847. 



Pelecypoda. 



We may consider the three genera of Pelecypoda that occur in the 

 Inle basin together. They are Physunio of the family Unionidae, Cor- 

 hicida and Pisidium of the family Cyrenidae. Corbicida is the only 

 one of these represented, so far as we know, in the deposits of the 

 ■district and it is only found in quite superficial deposits. 



Two species of Physunio are found living in the district, one (P. 

 ferrugineus) in the open parts of the lake, the other (P. micr after oides) 

 in the streams that run into it. A feature of the genus is the production 

 of a triangular " wing " on the dorsal surface ; as I have shown above, 



, this wing is used by the lake-form in ploughing its way through semi- 

 liquid mud. The structure exhibits, in this and other species, a great 

 difference in shape and relative size at difTerent periods of growth, being 

 much smaller in very young and very old shells than it is in those which 



-are just attaining maturity. Otherwise, P. ferrugineus shows only 

 slight variations in outline and proportion and in the structure of the 



1 Heude, Mem. Nat. Hist. Emp. Chinois I, pi. xl (1880-1890). 



2 V. Martens in Weber's Zool. Ergebn. Niederl. Ost.-Ind. IV, p. 25, pi. ii (1897). 

 » P. and E. Sarasin, Sussio.-Moll. Celebes, p. 62, pi. x (1898). 



* Benson, Journ. As. Soc. Bengal V, p. 745 (1836). He does not state the precise 

 locality of his specimens, but the Indian Museum possesses others collected in Manipur 

 bj' Godwin-Austen. 



* Forbes, Edinb. Phil. Journ. XLII, p. 271, pi. ii (1847). See also Newton, who gives 

 other references : Proc. Mai. Soc London IX, p. 363 (1911). In the Tertiary beds of 

 Eastern Europe other families of molluscs, especially the Neritidae and the Hydrobiidae, 

 exhibit a similar evolution, while in the recent fauna of the Yang-tse, which possesses a 

 remarkable resemblance to the later Tertiary freshwater faunas of Eastern Europe, 

 peculiar shells occur in the Hydrobiidae in many respects analogous to those of the Ter- 

 tiary Viviparae or of the living Taiae. 



