I066 I'HVSUXIO 



pseudocardinals and laterals compressed, lamellar, lightly 

 curved ; muscle scars shallow ; nacre pale bluish, iridescent. 



Length O0-68, height 37-41. diam. 23-25 mm. 



Siam ; Cambodia. 

 Unio micropterus Morelkt, Jl. de Conch., XIV, 1866, p. 63; 



Ser. Conch., IV, 1875, p. 349, pi. xv, fig. 6. 

 Physunio micropterus Simpson, Syn., 1900, p. 831. — Haas, 



Conch Cab., L'nio, 1912, pi. 33, fig. 9. 



I cannot be certain as to the relationships of this species as 

 I know nothing whatever of the beak sculpture, and the form 

 is more distinctly rhomboid than in any of the species I have 

 placed in the group. 



Physunio scmialatus (Deshayes and Julien). 



Shell irregularly obovate, thin, scarcely inflated, inequilat- 

 eral ; beaks full, and somewhat elevated, their sculpture not 

 known ; posterior ridge rounded, nearly straight, ending be- 

 hind in a rounded point about on the median line ; hinge line 

 straight, carried out into a small wing behind ; anterior end 

 narrowed, rounded, angled above ; base line lightly curved, 

 very full and widely rounded behind the middle ; dorsal slope 

 obliquely truncate behind ; surface with delicate growth lines 

 with a slight radial ridge on the posterior slope and a row of 

 minute wrinkles or folds along it with a few feeble plications 

 above it ; epidermis greenish-olive, brilliant ; teeth greatly com- 

 pressed, lamellar ; laterals curved, apparently triple in the left 

 valve ; nacre yellowish, brilliant. 



Length 'P>^, height 53, diam. 24 mm. 



Siam ; Cambodia. 

 Unio semialatus Deshayics and Julien, N. Arch. Mus., X, 



1874, p. 123, pi. VI, figs. I, 2. 

 Physunio semialatus Simp.son, Syn... 1900, p. 831. — Ha.\s, 



Conch. Cab., Lhiio, 1912, pi. 34, figs. 1-2. 



This may be a Hyriopsis, but without knowing anything of 

 the beaks I cannot tell. Deshayes says it seems to be equally 

 related to Unio discoideus Lea and U. snperbus.. The row 

 of minute folds down the dorsal slope recalls a character of 

 Cristaria plicata and Hyriopsis ciumingii, but they are a great 

 deal finer than in either of those species. 



