238 DESCRIPTION OF 



ruUginosus, when it is rayed at all, are usually very obscure. In the cardinal 

 teeth they differ also ; those of the ruUginosus being flatter, and more spread out. 

 In its yellow epidermis and rays, the Bigbyensis resembles the U. oviformis, 

 Con. That shell, however, is more oblique, and it may at once be distinguished 

 by the large ovate lunule; the Bigbyensis apparently possessing none. 



Unto crocatus. Plate 22, Y'm. 52. 



Testa ellipticd, inflatd, in(Bquilaterali, postict angulatd; valvulis tenuibus; natibus prominentibus ; 

 epidermide croced, radiatd, nitidd ; dentibus cardinalibus parvis ; lateralibus longis curvisque ; marga- 

 rita salmonis colore tincta et iridescente. 



Shell elliptical, inflated, inequilateral, angular behind ; substance of the shell thin ; beaks prominent ; 

 epidermis saffron-coloured, radiated, shining ; cardinal teeth small ; lateral teeth long and curved ; nacre 

 salmon-coloured and iridescent. 



Hab. Savannah River, Geo. T. R. Dutton. 



My Cabinet, and Cabinet of Mr. Dutton. 

 Diam. .8, Length 1.2, Breadth 1.8 inches. 



Shell elliptical, inflated, inequilateral, angular behind, substance of the shell 

 thin, thicker before; beaks prominent; ligament rather thin and short; epider- 

 mis saflfron-coloured, smooth and shining, with linear rays and numerous 

 regular lines of growth; cardinal teeth small, single in the right and double in 

 the left valve; lateral teeth long and curved; anterior cicatrices distinct; poste- 

 rior cicatrices confluent; dorsal cicatrices placed in the centre of the cavity of 

 the beaks; cavity of the shell deep; cavity of the beaks deep and angular; nacre 

 salmon-coloured and iridescent. 



Remarks. — Two specimens of this species are before me. One has nume- 

 rous capillary lines radiating from the beak, while the other has but few and 

 very indistinct ones. It is most nearly allied perhaps to U. ochraceus, Say ; but 

 may be distinguished by the colour of the epidermis, by the teeth being thicker, 

 and by the inflation of the umbones. The posterior slope is without rays, and 

 is somewhat rough. 



