1918.] N. Annandale: MoUvsrs of flip Ivle Lnhe. 



149 



the shell-form of aquatic Gastropods is concerned. The three species 

 now livino- in the Inle Basin belong to two groups, that of L. pervia 

 and that of L. howelli. These groups are separated not only by the 

 form and structure of the shell but also by those of the buccal 

 armature. To the first group belongs L. andersoniana, while the group 

 of L. howzlli is represented by L. shanensis and L. mimetica. 



a 



c 



d. 



Fig. 4. — Shells of Limnaea illustrating differences between pond and stream forms 

 a. Pond form of L. andersoniana from a pond near Yawn^hwe. 

 6. Stream form of the same species from a small stream at Fort Stedman. 

 c. L. ovata from Germany. 

 (1. L. jieregra from Germany. 



The figures are not drawn to scale. Figs. C and D are after Thiele. 



Two phases of L. andersoniana are found both in the Inle basin and 

 in Yunnan. In the Shan States at any rate, one of these phases lives 

 in ponds, while the other has been found only in a small stream. More- 

 over, the differences between the shells of the two phases are precisely 

 comparable to those between the European L. ovata and L. peregra, 

 forms still accepted by German conchologistsi as distinct species, al- 

 though it has been shown that it is possible to transform the direct 

 offspring of one into the other by transferring the eggs of L. ovata into 

 running water, or those of L. peregra into still water. 2 In both cases 



1 Thiele states that both forms are found in still and slow-running water but it is 

 not improbable that the form of the shell becomes fixed at an early age and that a 

 later transference would not alter it. See Thiele, " Mollusca" in Braucr's ASwssjwsser- 

 fmina DeutscUands, XIX. pp. fi, 7 (1909). 



^ See Cooke in the volume (III) on Mollusca, etc. in the Cambridge Natural History, 

 p. 93 (1895). I have not been able to refer to Hazay's work on the subject. 



