﻿TIYRIOPSTS 213 



Unio hotisei Lea, Pr. Ac. N. Sci. Phila., VIII, 1856, p. 92 ; 



Jl. Ac. N. Sci. Phila.. Ill, 1858, p. 291, pi. xxiii, fig. 3; Obs., 



VI. 1857. p. IT. pi. XXIII, fig. 3. — SowERBY, Conch. Icon., 



XVI, 1866, pi. XLVIII. fig. 260. 

 Mari^aron (Unio) hoitsei Lka, Syn., 1870, p. 28. 



The epidermis is olive-green when young and brown in the 

 adult shell ; in old specimens the nacre is very thick anteriorly. 

 A single old valve in the Lea collection is 185 millimeters in 

 length, and its pseudocardinals are heavv and consist of strong, 

 irregular cross ridges ; the laterals are short and remote. Unio 

 honsei of Lea is. I am sure, only the young of the above. 

 There are scarcely any traces of plications on the posterior 

 slope. ' ^ 



HyRiorsis sutrangensis (Morlet). ' j 



Shell large, obovate and subrhomboid, thick, subinflated, 

 with a blackish epidermis, which is concentrically striated and 

 lamellate behind ; hinge and basal line slightly curved : behind 

 the hinge the shell is angled, and below this it is obliquely 

 truncated and sinuous ; anterior end rounded and narrowed ; 

 posterior ridge low ; beaks well forward, their sculpture not 

 observed ; right valve with two rather short, thick, crenulate 

 pseudocardinals and one long, thin lateral ; left valve with one 

 pseudocardinal and two laterals ; anterior muscle scars deep, 

 with two well-marked, smaller scars at each ; posterior scars 

 shallow ; dorsal scars five or six ; nacre whitish, bluish behind. 



Length 140. height 62. diam. 34 mm. 



Sutrang River, Siam. 

 Unio sutrangcnsis Morlet, J. de Conch., XXXX'II, 1889, p. 



195, pi. IX, fig. 3. 

 Hyriopsis siiiyaui!;ensis Simpson, Syn.. 1900, p. 580. 



This species probably belongs in the genus Hyriopsis, 

 though Morlet believes it to be near to Unio scutum. Nothing 

 is known of its beak sculpture. 



Hyrtopsis eulvaster (Drouet and Chaper). 



Shell elliptic, subrhomboid, rather short, subinflated, thin, 

 inequilateral ; post-dorsal part somewhat elevated, and almost 

 wing-like; anterior end somewhat narrowed, truncate above. 



