﻿230 CKISTARIA 



posteriorly ; epidcrnris smooth, somewhat rayed ; hinge teeth 

 very fcel)ic. often nearly wanting; dorsal scars few; muscle 

 scars taint. Animal nnknown. 

 Tvi)c. SxDif'liynota discoidea Lea. 



CuisTAUiA iMSCoiDiiA (Lea). 



Shell nearly evenly elliptical, not inflated, thin hut strong, 

 lenticular; the beaks compressed, their sculpture consisting of 

 feeble concentric ridges; with a low wing behind, which is 

 straight on its dorsal edge ; anterior end evenly rounded, wing- 

 less ; base line regularly curved ; the shell ends posteriorly in 

 a blunt point at the median line; posterior ridge almost want- 

 ing ; surface nearly smooth, yellowish-green, with a wide, faint, 

 concentric, green band near the edge, the umbonal region pale 

 brownish-green, very feebly rayed throughout ; pseudocardi- 

 nals wanting or reduced to mere raised threads, laterals scarce- 

 ly developed, one in each valve ; beak cavities shallow, with 

 one or two scars in each ; posterior dorsal plications wanting 

 or only shown as mere vestiges ; muscle scars shallow, the 

 posterior crescentic ; nacre bluish-white, minutely radially gran- 

 ulous ; iridescent behind. 



Length 90, height 55, diam. 28 mm. 

 Syniphynota discoidea Lea, Tr. Am. Phil. Soc, V, 1834, p. 



75, pi. XI, fig. 33; Obs., 1, 1834, p. 187, pi. XI, fig. 33. 

 Barbala discoidea II. and A. Adams, Gen. Rec. Moll., H, 1858, 



p. 501. — Chknu, Man., 1859, II, p. 145, fig. 716. 

 Dipsas discoidea Kustick, Conch. Cab. I'uio, 1862, p. 306, pi. 



c. tig. 1. 

 Cristaria discoidea Simpson, Syn., 1900, p. 585. 

 Margarita fUnio) discoideus Lea, Syn.. i83'^i. p. 47; 1838, p. 



28. 

 Unio discoideus Hani,ey, Biv. Shells. 1843. p. 214, pi. xxi, 



fig:- 57- 



Margaron (Unio) discoideus Lea. Syn.. 1852. p. 46; 1870, p. 



74- 

 Unio tenuis Gray. Oriflfith's Cuv., XII. 1834. p. 601 (index), 



pi. XXIV. fig. 2. 



