﻿UNITED STATES AND NORTHERN MEXICO. 347 



distinct and well impressed ; dorsal cicatrices placed under the plate behind the car- 

 dinal teeth; cavity of the shell very shallow and wide; cavity of the beaks rather 

 shallow and angular ; nacre white or yellowish and iridescent. 



Remarks. — Several specimens of different ages were received from Professor Tuomey, 

 and a single one from Mr. Thornton. The specimen of the latter is rather more com- 

 pressed, a little more yellow in the epidermis, and has the teeth and thicker portions 

 of the valves of a yellowish tint. In outline it is near to ruhiginosus (nobis), and to 

 Meredithii (nobis); but it is not sulcate like the latter species, nor are the marks of 

 growth so close, or the posterior slope so high. It is not so triangular as ruhiginosus, 

 nor is the umbonial slope so angular, neither is it so large a species. The widest of 

 eight specimens before is but 1*7 of an inch. The rays are delicate and of a fine 

 green. In nearly all the specimens the anterior and posterior portions are without 

 rays. 



Unio modicellus. PI. 57, fig. 172. 



Testa laevi, subobliqua, inflata, postice subbiangulata, insequilaterali ; valvulis subcrassis, anticc crassioribus • 

 natibus prominentibus; epidermide vel lutea, vel luteo-oliva, obsolete radiata; dentibus cardinalibus 

 parvis, compresso-conicis, crenulatis, in utroque valvulo duplicibus ; lateralibus curtis, crassis subrectisque ; 

 margarita alba, postice aurea et iridescente. 



Shell smooth, suboblique, inflated, somewhat biangular behind, inequilateral ; valves 

 rather thick, thicker before ; beaks rather prominent ; epidermis yellow or olive yel- 

 low, obtusely radiate ; cardinal teeth small, compressed conical, crenulate, double in 

 both valves ; lateral teeth short, thick and nearly straight ; nacre white, golden color 

 behind and iridescent. 



Proc. Acad. Nat. Sei. 1859, p. 171. 



Hah. — Connasauga Kiver, Bishop Elliott, and Chattanooga River, Georgia, T. Stew- 

 ardson, M. D. 



My cabinet and cabinet of Bishop Elliott. 

 Diam. -6, Length -8, Breadth 1 -1 inch. 



Shell smooth, suboblique, somewhat biangular behind and rounded before, slightly 

 impressed before and behind the umbonial slope, inequilateral ; substance of the shell 

 rather thick, thicker before ; beaks swollen and rather prominent ; ligament very 

 short and very light brown ; epidermis yellow or olive yellow, very obscurely radiate 

 before the umbonial slope, with distant marks of growth ; umbonial slope raised and 

 subbiangular ; posterior slope broad, with two raised lines, having a broad furrow 

 between on each valve ; cardinal teeth small, compressed conical, crenulate and 

 double in both valves ; lateral teeth short, thick and nearly straight ; anterior cica- 

 trices confluent and deeply impressed; posterior cicatrices distinct and rather slightly 

 impressed ; dorsal cicatrices situated on the underside of the plate posterior to the 

 cardinal tooth ; cavity of the shell rather deep and rounded ; cavity of the beaks 

 shallow and obtusely angular; nacre white, golden color behind and iridescent 



