﻿UNITED STATES. 71 



to the posterior portion, which is evidently made by a byssus. In the two closely 

 allied species acutissimus and Gonradicus (nobis,) I have elsewhere described the 

 byssus,* which remained perfect in adult species. There cannot, therefore, be any 

 question as to the fact that rubellinus is furnished with a byssus, even at its full ma- 

 turity, by which it anchors itself. 



Embryonic shell subovate pouch-shape ; color clear white. 



Remarks. — This is a very beautiful little species nearly allied to acutissimus and 

 Gonradicus. Several fine specimens were received from Bishop Elliott. The rays 

 are indistinct, and are formed partly by obscure arrowhead or zigzag markings, 

 which are plainer on the posterior half. The nacre is usually a fine red, but some- 

 times inclined to salmon color. The males (see the figure) are much constricted 

 behind and emarginate at base. The posterior third is usually furnished with small 

 folds which are sometimes crimped. 



Unto excavatus. PL 13, fig. 52. 



Testa lsevi, subtriangulari, valde innata, subaequilaterali, postice angulata ; valvulis subcrassis, antice crassi- 

 oribus ; natibus valde prominentibus et tumidis ; epidermide vel lutea vel luteo-oliva, polita, radiata, 

 antice subsulcata; dentibus cardinalibus magnis, erectis, conico-compressis, crenulatis, in utroque val. 

 vulo duplicibus ; lateralibus subbrevibus, lamellatis crassisque ; margarita alba et iridescente. 



Shell smooth, subtriangular, very much inflated, nearly equilateral, angular behind; 

 valves rather thick, thicker before, beaks very prominent and much inflated ; epider- 

 mis yellowish or yellow-olive, polished, rayed, subsulcate before ; cardinal teeth large, 

 erect, compressed-conical, crenulate, double in both valves ; lateral teeth rather short, 

 lamellar and thick, nacre white and iridescent. 

 Proc. Acad. Nat. Sci., 1857, p. 32. 



Hal. — Othcalooga Creek, Gordon County, Georgia, Bishop Elliott, and Etowah, 

 Georgia, Rev. Geo. White; Alabama River, Claiborne, Alabama, Judge Tait. 



My cabinet and cabinets of Bishop Elliott and Rev. Mr. White. 

 Diam. 2*2, Length 3, Breadth 4-1 inches. 



Shell smooth, subtriangular, very much inflated, nearly equilateral, angular behind 

 and obliquely rounded before ; substance of the shell rather thicker before ; beaks 

 very prominent, much inflated, incurved, and slightly undulate at the tip ; ligament 

 short and very thick ; epidermis yellow and yellowish olive, polished, rayed, and with 

 very distant lines of growth ; umbonial slope raised into a sharp angle ; cardinal teeth 

 large, erect, compressed-conical, crenulate, double in both valves ; lateral teeth rather 

 short, lamellar, thick and slightly curved ; anterior cicatrices distinct, both large 

 and deeply impressed ; posterior cicatrices nearly distinct ; dorsal cicatrices placed on 

 the under side of the cardinal teeth and the plate ; cavity of the shell very deep, 

 excavated and rounded ; cavity of the beaks very deep and subangular ; nacre white, 

 sometimes pinkish and iridescent. 



*Proc. Acad. Nat. Sci. Sept., 1856. 



