﻿HYRIOPSIS 215 



Group of Hyriopsis -vagula. 



Shell elliptical, with a rather high, posterior wing, moder- 

 ately solid, with two slight posterior ridges and a sulcus above 

 them at the juncture of the wing. 



Hyriopsis VAGULA (Fischer). 



Shell irregularly elliptical or subrhomboid, subcompressed, 

 solid, with a low, curved posterior ridge; beaks full and in- 

 flated for a member of this genus, their sculpture not seen; 

 surface rich olive-brown; dorsal line nearly straight; outline 

 of posterior slope truncated, ending in an obtuse angle at the 

 summit of the wing; anterior end of the shell rounded; pos- 

 terior end more narrowly rounded ; base evenly curved ; nacre 

 whitish-salmon in the cavity of the shell. 



Length loo, height over all 80 mm. 



Siam. 



Unio subtrigonus Sowerby, Conch. Icon., XVI, 1867, pl- LViii, 

 fig. 292. 



Margaron (Unio) subtrigonus Lea, Syn., 1870; p. 28. 



Unio (Monocondyicea) cambojensis Sowerby, Conch. Icon., 



XVI, errata. 

 Pseudodon cambojensis Morelet, Ser. Conch., IV^, 1875, P- 



336. 

 Unio lamellatus Haneey and Theobald, Conch. Ind., 1876, 



p. 5, pi. IX, fig. 6. 

 Unio vagidus Fischer, Bull. Soc. Autun., IV. 1891, p. 22^. 

 Hyriopsis I'agithis Simpson, Syn., 1900, p. 580. 



The above description is taken from Sowerby's figure and 

 description. Sowerby says nothing whatever of the teeth or 

 muscle scars, and I cannot therefore be certain as to its sys- 

 tematic position, but believe with Fischer that it is near the 

 Unio myersianus Lea. Sowerby published the species in the 

 Conchologia as Unio subtrigonus, but the name was preoccu- 

 pied by Deshayes. In the errata he changed it to Unio (Mon- 

 ocondylcea) cambojensis, believing it to equal Petit's species. 

 It is certainly not that shell and I therefore accept Fischer's 

 name for it. 



