I9I9-] 



B. Prashad: Asiatic Unionidae. 



405 



of M. vondembuschiana. Simpson considers Mousson's species 

 Alasimodonta crispata synonymous with M. vondembuschiana, 

 but in my opinion it is a distinct species, as it was also considered 

 to be by von Martens.^ 



Monodontina, Conrad. 



As already stated, the genus was established by Conrad for 

 Lea's species Margariiana vondembuschiana, with the following 

 description : "Hinge with an obtuse rounded tooth immediately 

 below the beak." It may be redescribed as follows : — Shell rather 

 thin, rhomlDoid ovate, rounded in front, truncated posteriorly, 

 with the result that the posterior margin is nearly straight ; with 

 a narrow wing and a feebly developed posterior ridge ; in young 

 specimens a second ridge also visible above the posterior ridge ; 



Text-fig. 1. — Jlfonodoiitiiui vomlembiiscliiaiia, \'ar, chaperi, hinge and 

 muscle-scars. 



umbo compressed, beak sculpture con.sisting of concentric zig-zag 

 lines ; shell practically smooth except for lines of growth ; hinge- 

 line straight (fig. i) ; a single smooth cardinal tooth (T) in each 

 valve, that of the right valve situated just in front of the umbo 

 and fitting in front of that of the left valve ; lateral tooth represent- 

 ed b}^ a feebly developed ridge in each valve, its posterior limit 

 having a triangular brownish scar containing a prolongation of the 

 hinge-ligament; the two anterior muscle-scars prominent, uniting 

 with one another and having very irregular outlines ; posterior 

 muscle-scars very faint and separate ; nacre bluish, somewhat iri- 

 descent with a brownish marginal line running parallel to the 

 border at a little distance from the edge. 



The animal of the Sumatran form (fig. 2) has the inner pair of 

 gills very much wider than the outer throughout their entire length. 



' Malakol. Blatter, XIV, p. 13 (1867). 



