﻿3IO p[,.\Gioi,.\ 



the [)incliccl-up posterior ridge; surface ratlier smooth, feebly 

 shining, pale dirty or smoky-greenish, with a pattern of broken 

 rays, which are often made up of irregular blotches or zigzag 

 markings ; this zigzag pattern is sometimes developed between 

 the rays. Left valve with two com})ressed pseudocardinals and 

 two laterals ; right valve with one pseudocardiiial and one 

 lateral ; beak cavities very shallow ; muscle scars small, the 

 hinder circular ; nacre bluish. The female shell is quite full 

 in the post-basal region and nmch more blunt behind than the 

 male. 



Length (male) 45, height ij, diam. 16 mm. 



Length (female) ^^y, height 23, diam. 14 mm. 



Eastern Texas, northward probably into Kansas. 



Type locality. Rutersville, Texas. 

 JJnio inacrodon Lea. Pr. Ac. N. Sci. Phila., IIL 1859, p. 154; 



Jl. Ac. N. Sci. Phila., V'L 1862, p. 193, pi. xxvi, fig. 262; 



Obs., IX, 1863, p. 15, pi. XXVI, fig. 262. — PSowERHY, Conch. 



Icon., XV'I, 1868. pi. Lxxxviii, fig. 437. 

 Margaron (Unio) inacrodon Lka. Syn., 1870, p. ^^y. 

 Plagiola inacrodon Simpson. Syn., 1900, p. 605. 



Less inliated and rather longer than P. donaciformis, the 

 color patterns less vivid and generally not quite as sharply 

 pointed behind. The female shell especially is quite blunt. 



Pr,Ar,ioi,A COGNATA (Lca). 



Shell elliptical, convex, solid, inequilateral, w itli a well-de- 

 veloped ]>osterior ridge and high b,eaks, wliich are sculptured 

 with a few delicate, doubly-looped bars : epidermis smooth, 

 shining, yellowish-green with a number of darker rays ; left 

 valve with two triangular, somewhat ragged, pseudocardinals, 

 the anterior one smaller, and two laterals, the upper the 

 smaller ; muscle scars deep ; beak cavities moderate and rather 

 shallow, sho\^•ing the dorsal scars ; nacre bluish white or sil- 

 very, iridescent and lliiniicr behind. 



Length 44, height 28, diam. 20 mm. 



Rio Salado, New Leon, Mexico. 



