1918.] N. Annandale: MoUuscs of the InU Lake. 143 



Part II.— PALAEONTOLOGICAL. 



The deposits in the Inle and He-Ho basins from which fossil and 

 siibfossil shells were obtained are of three classes : (1) cave-deposits, 

 (2) lake-deposits and (3) superficial deposits on the banks of streams 

 and in dried-iip marshes. 



Cave-Deposits. 



The cave-deposits were discovered in two small limestone caves 

 on the eastern slope of the valley of the Hsin-Dawng stream some three 

 miles east of the town of Yawnghwe. They are at a height of three to 

 five hundred feet above the level of the Inle Lake and in what was pro- 

 bably the basin of a small but deep subsidiary lake that dried up at a 

 period long before the He-Ho lake disappeared. Unfortunately there 

 are no precise data for fixing the age of the deposits, but it seems 

 legitimate at any rate to class the animal remains as fossil. These 

 remains were in or upon the surface of banks of red soil, the depth 

 of which was not ascertained. They consisted (apart from teeth of the 

 Tharain, Cervus eldi — probably those of a single individual) of shells 

 of Taia and Melania, those of the former genus being abundant but the 

 latter represented by a single specimen. In other words, the smaller 

 molluscs such as the Limnaeidae and Hydrobiidae that are likely to have 

 existed in the fauna are entirely absent, while the larger shells of more 

 expanded form are well represented. This is probably due to the fact 

 that shells of Taia when dry and full of air or gas float readily on the 

 surface of water, ^ while those of molluscs of smaller size or more con- 

 tracted shape such as Planorhis or Hydrohioides as a rule sink. If this 

 theory be correct the shells must have floated on the surface of a lake 

 or pool until they were stranded at the base of limestone rocks and there 

 been buried. Their unworn condition proves that they have not been 

 carried bv running water. 



The remains from these cave deposits represent the following 

 species : — 



Mammalia. Mollusca. 



Cervus cldi. Mekinia variabilis. 



Taia obesa. 

 Taia cylindrica. 

 Taia conica. 



These remains must have been contemporaneous, but it is by no 

 means improbable that the molluscs lived in different types of environ- 

 ment and were brought together in the manner indicated. The deer 

 and the Melania survive, the species of Taia are all extinct. 



Lake-Deposit. 



At the north-east corner of the He-Ho basin there is, between two 

 limestone spurs, a small plain through which the He-Ho river has cut 

 for itself a narrow but rather deep bed. On the north side of this bed 



^ This was observed both iu the Ir.le Lake and iii the He-Ho streams. 



