INSTITUTE OF SCIENCE, PHILADELPHIA. 93 



Surface radiately ribbed ; ribs narrow, about thirty in number, pro- 

 foundly squamous, the scales erectly vaulted, compressed and carinate, 

 or overlapping, on the posterior side, broadly flattened anteriorly, so as 

 to produce shallow cups, through which the ribs appear to pass. 



Height, 1.4 inches. 



This species most resembles among recent forms Cardinal consors 

 from the west coast of South America, which differs in the greater 

 number and closer imbrication of the scales on the posterior slope, and 

 in lacking the open cup-like forms of the anterior border; the elevated 

 dental plate is also less prominent. 



Hemicardium columba, nov. sp. Fig. 26. 



Shell (known only by the left valve) elevated, gibbous, carinated on 

 the umbonal slope ; posterior cordiform space profoundly hollowed ; 

 anterior border evenly rounded ; base slightly sinuous posteriorly, some- 

 what produced ; posterior border deeply emarginate ; beaks elevated, 

 transverse, the apex appearing as though directed to the rear ; cardinal 

 teeth two, enclosing a deep pit, the anterior one much the more promi- 

 nent ; lateral teeth lamellar, pyramidal ; entire surface of shell closely 

 ribbed, ribs echinated, about thirty-six in number, some thirteen of 

 which are on the posterior slope ; basal margin crenulated. 



Height, to summit of beak, four-fifths of an inch ; length, .7 inch. 



I have but two valves of this species, a near ally of the recent Hcuii- 

 cardiuin media of the southern coast, from which it can be distinguished 

 by its more upright form, the deeper hollowing of the posterior face, and 

 the more pronounced carination of the umbonal slope. 



Chama arcinella, L. 



Syst. Nat., p. 1139. 



Numerous in the banks below Fort Thompson. 



The individuals of this species vary in the fossil much as they do in 

 the recent form, the variation depending upon the convexity of the 

 valves, the disposition and thickness of the spines, the presence or ab- 

 sence of interstitial secondary radiating lines, etc. In the collections of 

 the Academy of Natural Sciences there are a number of Chama valves, 

 from Cape Fear River, North Carolina, which are marked in Conrad's 

 handwriting Arcinella spinosa. I am not aware that the species has ever 

 been described as such, but it is nothing other than an unusually spiny 

 variety of C. arcinella, and, doubtless, the form which is correctly re- 

 ferred in Emmons's North Carolina report to the living species. 



Chama crassa, nov. sp. Fig. 27. 



Shell thick, ponderous, cordiform, with a prominent sulcus descending 

 the posterior slope ; both valves very convex, the left one somewhat the 

 larger; beaks spirally twisted, much as \nlsocardia; the hinge-line (in 



