UNITED STATES AND NORTHERN MEXK'O. 20 



distinct ami wrll iiiipiessed ; dorsal cicatrices placed under llic pliitt" Ijcliiiul 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 rnfjujinoius (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 ruhif/iiiostf^, 

 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 arc without 

 rays. 



Unio modicellus. pi. 57, fig. 172. 



Testa laevi, subobli()uri, influta, postici subbiangulata, inaequilatcrali ; valvulis subcrassis, antici crassioribus • 

 natibus prominentibus; cpidcrmidc vcl lutca vcl lutco-oliva, obsolete radiata; detitibus cardinalibus 

 parvis, comprcsso-conicis, crenulatis, in utroquc valvule duplicibus ; latcralibus curtis, crassis subrcctisf|ue ; 

 iiiargarita alba, postice aurta 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, tliick and nearly straight ; nacre white, golden color 

 behind and iridescent. 



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



Eab. — Connasauga River, Bishop Elliott, and Chattanooga Rivtr, 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 obtii.sfiv anrfujar: nacre while, <:olden color behind and iridescent. 



