﻿UNITED STATES AND NORTHERN MEXICO. 371 



and without any undulations ; ligament very small and thin ; epidermis yellowish olive, 

 polished, rayed, with rather distant lines of growth ; umbonial slope slightly raised 

 and rounded; posterior slope raised into a slight carina ; cardinal teeth small, lamellar 

 and oblique ; lateral teeth rather long, lamellar and somewhat curved ; anterior 

 cicatrices distinct and well impressed ; posterior cicatrices confluent and slightly im- 

 pressed; dorsal cicatrices placed under the plate between the cardinal and lateral 

 teeth ; cavity of the shell rather shallow and rounded ; cavity of the beaks shallow 

 and subangular ; nacre bluish white and iridescent. 



Remarks. — A single specimen only has been received by the Smithsonian Institution 

 among the shells collected by Dr. Berlandier, and presented by Lieut. Couch. This in- 

 dividual is, I think, the young or about the half-grown of a small species. It is nearer in 

 outline and in the color and smoothness of its epidermis, as well as in its rays, to U. 

 amygdalum (nobis), than to any other species I am acquainted with ; but it may at once 

 be distinguished by its outline approaching more to rotundity. The nacre also differs 

 in being less pearly. The beaks are remarkable for being entirely without any undula- 

 tion of any kind, at least this specimen has no appearance of them. 



Unio Couchianus. PI. 66, fig. 196. 



Testa lsevi, quadrat a, inflata, biemarginata, ad latere sulcata, inaequilaterali, postice biangulala, antice 

 rotunda; valvulis crassis, antice crassioribus ; natibus prominentibus ; epidermide olivo-fusca, striata, 

 eradiata; dentibus cardinalibus subgrandibus, erectis, rugose- striatis, crenulatis; lateralibu3 sublongis, 

 crassis curvisque ; margarita argentea et valde iridescente. 



Shell smooth, quadrate, inflated, biemarginate, furrowed on the side, inequilateral, 

 biangular behind, round before ; valves thick, thicker before ; beaks prominent ; 

 epidermis olive brown, striate, without rays ; cardinal teeth rather large, erect, rugosely 

 striate and crenulate ; lateral teeth rather long, thick and curved ; nacre silvery white 



and very iridescent. 



Proc. Acad. Nat. Sci. 1860, p. 305. 



Hob. — Rio Salado, New Leon, Mexico. L. Berlandier, M. D. 



My cabinet and cabinet of Smithsonian Institution. 

 Diam. '9, * Length 1-3, Breadth 1*8 inches. 



Shell smooth, quadrate, inflated, biemarginate, furrowed on the side, inequilateral, 

 biangular behind, round before ; substance of the shell thick, thicker before ; beaks 

 prominent, inflated ; ligament rather short and thick ; epidermis olive brown, striate, 

 without rays and with rather distant marks of growth ; umbonial slope biangular and 

 flattened ; posterior slope wide, raised into an angular carina, with an unequal im- 

 pressed line in each valve from the beaks to the posterior margin ; cardinal teeth rather 

 large, erect, rugosely striate, crenulate, thick and disposed to be trifid in the right valve ; 

 lateral teeth rather long, thick and curved ; anterior cicatrices distinct and very deeply 



