﻿212 iivKiorsis 



Group of flyridpsis mycrsiana. 



Shell rather solid, thickened in front ; posterior ridge rather 

 low ; heaks comjiressed, the sculi)ture consisting, apparently, of 

 a few rather faint, irregular ridges, sometimes slightly nod- 

 ulous. 



Hykiopsis myeksiana (Lea). 



Shell large, elliptical or ohovate, subcompressed or com- 

 pressed, solid when old, with a small anterior wing and a high, 

 ragged posterior wing when young, which is lost in old age ; 

 posterior ridge well developed, sometimes angulated, and there 

 are often one or two faint ridges on the posterior slope ; beaks 

 low. raised a little above the hinge line, subcompressed, with 

 faint, horizontal ridges, occasionally .slightly nodulous ; left 

 valve with two or three compressed, elongated, somewhat un- 

 even pseudocardinals and two curved laterals; right valve 

 with two pseudocardinals. the lower higher, and one lateral ; 

 when the shell becomes old the laterals are remote and the 

 pseudocardinals become split across into numerous irregular 

 denticles ; beak cavities shallow ; muscle scars of the cavities 

 in a diagonal row; anterior adductor scars small, impressed; 

 posterior scars shallow ; nacre white or tlesh-colored, often iri- 

 descent. The shells generally end in a wide, faint biangulation 

 behind ; in some of these the biangulation is mostly below the 

 median line, and the post-basal line is not much extended ; in 

 others the point is midway up the shell and there seems to 

 be a marsupial swelling. 



Length 165, height 95, diam. 45 mm. 



Siam ; Cambodia. 

 Unio mycrsianus Lba, Pr. x\c. N. Sci. Phila., VIII, 1856, p. 



92 ; Jl. Ac. N. Sci. Phila., IIL 1857, p. 290, pi. xxii, fig. 2 ; 



Obs., VI, 1857, p. 10, pi. XXII, fig. 2. — SowERBY, Conch. 



Icon., XVI, 1866, pi. I., fig. 265. 

 Margarnn (Unio) mycrsianus Lea, Syn., 1870, p. 28. 

 Mctitptera myersianns Morlet, J. de Conch., XXXVII, 1889, 



p. 165. 

 II\nof>s\s myersianns' Simpson. Syn., 1900. p. 580. 



