No. 89.] 91 



creased by implantation on the ventral valve : entire surface radiatingly striate. 



The specimen described is a little more than half an inch in length, and has the 

 appearance of a mature shell. It is readily distinguished from other Strophodoxtjs 

 described, by the strong rounded phcations of the surface. 



Geological formation and locality. In the rocks of the age of the Hamilton 

 group, near Iowa city. From Rev. TV. H. Barris. 



TROPIDOLEPTUS.? OCCIDENS ( n.s.). 



Shell semielliptical, longer than wide, concavo-convex; cardinal area very narrow 

 and linear : beak of ventral valve extending a little beyond the hinge-line. Sur- 

 face marked by twelve elevated angular plications, of which two central ones on 

 the ventral valve are a little stronger and more elevated, while a single central 

 one on the dorsal valve is a little depressed. The substance of the shell is silici- 

 fied : it appears to have been originally punctate. 

 I refer the species with some hesitation to the Genus Tropidoleptus, since the 



condition of the only specimen known does not admit of satisfactory determination. 



It is a matter of interest to discover other species of this peculiar genus. 



Geological formation and locality. In strata of the Hamilton group, near Iowa 



city. From Rev. W. H. Barris. 



CONOCARDIUM EBORACEUM ( n.s.). 

 Shell subovate, gibbous; anterior end obliquely truncate, the umbonial slopes 

 angular and flattened or concave within, the joining edges of the shell produced; 

 posterior end conical, scarcely constricted behind the beaks; umbones angular; 

 hiatus rounded anteriorly, narrow and elongate, reaching nearly the whole 

 length of the shell, and strongly denticulate on the inner margins. Surfaces can- 

 cellated by radiating and concentric striae, which are nearly equal upon the 

 upper part of the shell; while on the lower part the concentric striae become 

 strongly lamellose, and the radiating striae are obselete. 



This shell is somewhat equilateral, in having the anterior end on the base ex- 

 tending as far beyond the beaks, as the distance from the beaks to the posterior 

 extremities. The cancellated structure above and strong lamellese concentric striee 

 below, with the extreme hiatus, are distinguishing features. 



Geological formation vnd locality. In shales of the Hamilton group : in York, 

 Livingston county, New-York. 



CONOCARDIUM VENTRICOSUM ( n. s.). 



Shell extremel}'- ventricose, the width and thickness of the two valves being equal 

 to or greater than the height from base to beak, while the length is about equal 

 to the thickness. Beaks rising above the hinge-line, incurved : hinge-line straight; 

 anterior end almost vertically truncate, and sometimes abruptly and obtusely 

 rounded, usually slightly concave between the umbonial slope and the edges of 

 the sliell, posteriorly constricted just behind the beaks, and produced in a short 

 subconical extension : the hiatus on the lower side is narrow and short, rounde(? 

 at the posterior extremity. Surface of the bod}'- of the shell, and a part of the 

 posterior slope, marked. by slender radiating ribs, which become double below 

 their origin, and again coalesce at or near the edge of the shell; or the ribs may 

 be described as simple, with a sharp deep groove throughout the greater part of 

 their length : ribs on the anterior slope simple. 

 This is a pretty little species, remarkable for its great ventricosity and for the 



character of its ribs. 



Geolagical formation and locality. In limestone of the age of the Hamilton 



group : near Iowa city, Iowa. From Rev. W. H. Barrts. 



