﻿354 NEW UNIONIDjE OF THE 



Unio planicostatus. PI. 59, fig. 179. 



Testa laevi, elliptica, compressa, ad latere subplanulata, valde inaequilaterali, postice obtuse biangulata, antice 

 rotundata; valvulis tenuibus, diaphanis, antice" paulisper crassioribus; natibus prominulis, ad apices un- 

 dulatis; epidermide olivacea, undique radiata; dentibus cardinalibus parvis, conicis, crenulatis, in 

 utroque valvulo duplicibus ; lateralibus longis, lamellatis subcurvisque ; inarg ita vel caeruleo-alba 

 vel purpurascente et valde iridescente. 



Shell smooth, elliptical, compressed, flattened at the sides, very inequilateral, ob- 

 tusely biangular behind, rounded before ; valves thin, sem transparent, a little 

 thickened before ; beaks slightly prominent, undulate at the tips ; epidermis olivace- 

 ous, radiated over the whole disk ; cardinal teeth small, conical, crenulate and double 

 in both valves ; lateral teeth long, lamellar and somewhat curved ; nacre bluish white 

 or purplish and very iridescent. 



Proc. Acad. Nat. Sci. 1860, p. 92. 



Hab. — Tuscumbia, Alabama. L. B. Thornton, Esq. 



My cabinet and cabinet of Mr. Thornton and Mr. Pybas. 

 Diam. *6, Length 1*2, Breadth 2-2 inches. 



Shell smooth, elliptical, compressed, flattened at the sides, very inequilateral ; ob- 

 tusely biangular behind, rounded before ; substance of the shell thin, semitransparent, 

 a little thickened before ; beaks slightly prominent, minutely undulate at the tips ; 

 ligament, rather long, thin, dark brown ; epidermis olivaceous, rather dark, radiated 

 over the whole disk; umbonial slope slightly raised and obtusely rounded ; poste- 

 rior slope narrow, raised into a small keel and with an impressed furrow which causes 

 an emargination on the superior posterior margin ; cardinal teeth small, conical, crenu- 

 late and double in both valves ; lateral teeth long, lamellar, and somewhat curved ; 

 anterior cicatrices distinct and moderately well impressed ; posterior cicatrices confluent 

 and very slightly impressed ; dorsal cicatrices placed in the centre of the cavity of 

 the beaks and on the underside of the plate; cavity of the shell very shallow and 

 wide; cavity of the beaks very shallow and obtusely angular; nacre bluish white or 

 purplish and very iridescent. 



Remarks. — I received a number of this species from Mr. Thornton, several of which 

 are females and smaller than the males. In outline it is very near to exiguus (nobis), 

 but it is rather more oblique, thinner and less polished, some of the specimens being 

 almost striate. The specimen figured is the largest among all those received, and has 

 fine green rays all over the surface of the disk. Some of the specimens are yellowish 

 towards the anterior margin and some are quite green on the posterior half, by the 

 rays closing together and giving that tint to this portion of the epidermis. Two of 

 the specimens are tinted slightly with purple in the teeth and the cavity of the 

 beaks. 



