1918.1 N. Annandale : Molluscs of the Inle Lake. 141 



The shape is variable (see figures). I figure on pi. XIX a series 

 showing different growth-stages as well as variation in old shells. 



Measurements of shells (in millimetres). 



Length of shell 

 Greatest depth of shell 

 Thickness of shell 



Type-specimen. M. 11290/2, Zoological Survey of India {Ind. Mus.). 



Habitat. — This mollusc is very abundant in the semi-liquid mud at 

 the bottom of the central region of the Inle Lake in water from 7 to 

 12 feet deep. Its position of rest in the mud is with the longer axis 

 vertically upright and the valves buried nearly as far as the posterior 

 end of the wing. It progresses through the mud by thrusting out the 

 foot downwards and forwards. This forces the whole animal in the 

 opposite direction and at the same time presses the dorsal edge of the 

 valves downwards. The foot is then withdrawn and the shell regains 

 its vertical attitude a little in advance of its former position. The 

 foot is thrust out again and the movement repeated. The result is that 

 the mollusc progresses with a see-saw motion, dorsal edge in front, the 

 wing assisting greatly in overcoming friction by acting as a kind of 

 ploughshare. The posterior end of the valves is often covered with a 

 massive brown alga of the family Rivulariaceae. 



The glochidium is parasitic on the fins of Barilius auro^mrpureus, 

 mihi. 



Suborder Conchacea. 



Family CYRENIDAE. 



Genus Corbicula, Mergerle. 



Corbicula noetlingi, v. Martens. 



Plate xix, fig. 12. 



1899. Corbicula Noetlingi, von Martens, op. cit., p. 47, pi. iv, figs. 7-9. 



Shells from the Inle and He-Ho basins differ from those figured 

 by von Martens in being somewhat longer. There is, however, sotne 

 individual variation in this respect, and probably greater plasticity. 

 Shells from Thamakan (alt. 4,000 feet) approach the typical form in 

 shape more nearly than do those from the Inle basin. 



Measurements of shells {in millimetres). 



Specimen A is from Thamakan, specimen B frcm the Yawrghwe river, while 

 specimen C was found subfossil in the superficial deposits (f the He-Ho plain; 

 specimems D and E, an adult and a yourg shell, are recent and from the same 

 locality as C. 



