1918.] N". Annandale: Mollvscs of the Inle Lake. Ill 



arge size, darker colour, less extreme fragility, non-rimate character 

 and non-angulate anterior margin. How close the resemblance is in 

 other respects is shown clearly by figs. 9-11 on plate x. 



It is difficult to see how this resemblance can be anything but for- 

 tuitous. It can be of no protective value to animals that never meet, 

 have entirely different habits and probably different enemies. It can- 

 not be due to convergence, to use the term in its technical sense, be- 

 cause of the difference in habits. It is well that attention should be 

 called to apparently fortuitous resemblances of the kind, for they are 

 apt to be ignored by students of mimicry — a series of phenomena as 

 to the meaning and causation of which I must confess myself, after 

 nearly twenty years' experience of tropical nature, in an agnostic frame 

 of mind. 



Limnaea ? prox. ovalis, Gray. 

 Plate x, fig. 3. 



I am unable to assign two fossil specimens from the old lake-deposit 

 in the He-Ho plain to any described species but think it probable that 

 they represent one allied to L. ovalis (pi. x, fig. 3). They are not 

 unlike some dwarfed shells of L. ovalis from pools of brackish water 

 in Orissa, but differ in the almost complete bilateral symmetry of the 

 body- whorl and in the very long aperture. With such imperfect material 

 it is best not to give the form a name. 



Genus Planorbis, Geoffroy. 



Living specimens of five species of this genus were found in the 

 Inle Lake, while the shells of a sixth are not uncommon in the super- 

 ficial deposits of the He-Ho plain. These six species fall into three 

 of the subgenera or groups into which the genus has been divided, viz., 

 Planorbis, s.s. ; Gyraulus, and Segmentina. They may be distributed 

 into these groups as follows : — Planorbis exustus to Planorbis s.s., 

 P. sai(jonensis (subfossil), P. velifer, sp. nov. and possibly P. trochoideus, 

 which lacks the characteristic internal partitions of the shell of Seg- 

 mentina, to Gyraulus ; P. calathus and P. caenosus to Segmentina. 



Planorbis exustus, Desh. 



Plate xi, figs. 1, la. 



1834. Planorbis exustus, Deshaves, Belang. Voy. Ind. Orient., Zool., p. 417, pi i, 



figs. 11-13. 

 1836. Planorbis Indicus, Benson, Journ. As. Soc. Benrjnl, V, p. 743. 



The shell of this species seems to differ from P. coromandelicus , 

 of which I have examined specimens from Bangalore, in its less inflated 

 whorls, darker and duller colour and in the fact that the angle at the 

 lower end of the mouth is less produced. Shells from the Kashmir 

 lakes, from a small pond of slightly brackish water on Barkuda Island 

 in the Chilka Lake, from the marginal zone of the Inle Lake and from 

 ponds and swamps at Yawnghwe and on the He-Ho plain are closely 

 similar ; except that the Kashmir examples are a little smaller. Speci- 



