114 Records of the Indian Museum. [Vol. XIV, 



figures. They are transparent and of a faint yellowish colour. Pos- 

 sibly they represent a dwarfed race of the species. 



P. caenosus has been found in Ceylon as well as in Northern India. 



Order PECTINIBRANCHIATA. 



Suborder Taenioglossa. 



Family MELANIIDAE. 



Genus Melania, Lamarck. 



1915. Tiara, Preston, oj}. cit., j). 10. 



The species found living in the Inle Lake and its basin belong to 

 two groups or subgenera, Striatella, Brot and Melanoides, H. and A. 

 Adams. The former is represented by the widely distributed and 

 plastic M. tuherculata, while we have of the latter M. terebra and a 

 race of M. haccata. A single shell of a form of M. variabilis, which 

 also belongs to this group, was found in a cave-deposit at Hsin-Dawng. 

 The only one of all these species that lives in the lake is M. tuherculata. 



Melania tuherculata (Miiller). 



Plate xii, figs. 1, 2. 



1874. Melania tuherculata, Brot, Melaniaceen in Martini and Chemnitz's Conch. 

 Cab. (ed. Kiister), ^. 247, pi. xxvi, figs. 11-1 lA. 



This is the most widely distributed species in the genus, ranging 

 as it does from the southern and eastern shores of the Mediterranean, 

 through Africa and Asia to China and North Australia. The shell is very 

 plastic in certain characters, notably in size, but also to a lesser degree in 

 shape and sculpture. I have before me a large series from many localities 

 in India and the neighbouring countries and also from Mesopotamia, 

 Palestine and China. Numerous varieties have been described, but our 

 collection seems to prove that as a rule the differences are directly due 

 to differences in environment rather than to locality. The tubercles 

 on specimens from southern Asia are, however, often less strongly 

 developed than in those from Palestine. I will discuss certain aspects 

 of the plasticity of this mollusc in dealing with the variation and evolu- 

 tion of the Inle shells. Here it will be sufficient to say that the shells, 

 both living and subfossil, from the Inle and He-Ho basins fall into 

 three phases : — (1) normal living shells of rather dark colouration, of 

 moderate size, not exceeding 25 mm. in length ; (2) subfossil shells 

 which were apparently also of dark colour, but are much larger (reach- 

 ing at least 35 mm. in length) and rather broader in the basal whorl ; 

 and (3) subfossil shells of very small size with the suture much im- 

 pressed. These do not exceed 16 mm. in length. 



The first group still lives both in the central region of the Inle Lake 

 and in the middle of the Yawnghwe river, while shells of the other two 

 occur at different points in the superficial calcareous and peaty 



