﻿HYRIOPSIS 211 



Hyriopsis dki.aportki (Crosse and Fischer). 



Shell with a high, irregular posterior wing, which is often 

 curled over at the top, and a smaller anterior wing like that 

 of a Prisodon, the median dorsal line nearly straight, showing 

 a part of the ligament, somewhat triangular, subsolid, scarcely 

 inflated, with a rather high, sharp or angled posterior ridge ; 

 beaks compressed, their sculpture consisting of 7 or 8 bars 

 running parallel with the hinge line ; epidermis pale, yellow- 

 ish-green or greenish-brown, scarcely shining; left valve, 

 when young, with two long, compressed pseudocardinals and 

 two curved laterals ; right valve with two pseudocardinals and 

 one lateral ; in some of the young there are three pseudocar- 

 dinals in each valve. As the shell grows older these break 

 up into vertical ridges and the laterals are shortened and be- 

 come remote ; beak cavities shallow with an irregular row of 

 pits ; anterior scars impressed ; posterior scars faint ; nacre 

 bluish-white, often blotched and dull. 



Length 130, height, without wing 70, with wing 100, diam. 

 35 mm. 



Cambodia, Siam. 

 Unio (Arconaia) delaportei Crosse and Fischer, J. de Conch.. 



XXTV, 1876, p. 327, pi. X, fig. I ; pi. XI, fig. 5. 

 Arconaia delaportei Morlet, J. de Conch., XXXVII, 1889, 



p. 165. 

 Hyriopsis delaportei Simpson, Syn., 1900, p. 580. 



The line of junction between the valves is not straight but 

 somewhat flexuous and the anterior or posterior end of the 

 shell may be flexed a little to the right or left, hence Crosse 

 and Fischer placed the species in Arconaia. There is a slight 

 anterior and posterior gap to the shells as in so many of the 

 winged American forms, and the shells seem to be somewhat 

 dimorphic. In two of the U. S. Nat. Museum specimens 

 there is quite a post-basal inflation and the posterior point is 

 elevated above the base line. In another the base line is a 

 little incurved medially and the posterior point is not at all 

 raised. There are traces of plication on the post-dorsal region 

 in most shells and the escutcheon is very large. 



