Rathbiin.] 254 [Decomber 16, 



latter of which is often nearly straight and about at right angles to 

 the hinge. The anterior and ventral margins together form a single, 

 quite regular curve, uniting, somewhat abruptly with the posterior 

 margin. 



Beaks small, acute in the interior moulds, strongly incurving and 

 inclining moderately forward. Their apices are situated a little an- 

 terior to the middle and ai'e approximate. Valves most convex jiisjt 

 above the centre, and arching rather strongly from the ventral mar- 

 gin to the beaks. The most prominent line of curvature of the shell 

 passes obliquely downward and backward fi'om the beak toward the 

 lower posterior angle, sometimes not far posterior to the middle, 

 at others about one-third the length from the posterior margin, 

 thus giving to the shell a slightly oblique appearance. The curva- 

 ture across the valves, from the anterior "to the posterior margin, is 

 very strong and always more abrupt posteriorly. Sometimes the 

 posterior slope is neai-ly straight, and the valves are then slightly an- 

 o-ular along the most prominent line of curvature. 



The shell is marked with prominent radiating plications only, about 

 twenty to twenty- five in number on each valve. I have "not been 

 able to detect any concentric lines. On the middle and larger por- 

 tion of the valves the plications are rather broad and flattened, and 

 separated by naiTOw, shallow, rounded depressions, sometimes scarcely 

 more than stria?. Toward the anterior and posterior extremities the 

 plications become regularly rounded and gradually narrower. At the 

 same time the interspaces, which are also rounded, increase in size 

 and near the margin exceed the plications in width. From the ante- 

 rior seven or eight plications arise minute spines, having rounded or 

 elonnrate bases and arranged in single rows. The plications nearest 

 the margin have six or eight spines, but these decrease in number to- 

 ward the middle, and become limited to the lower part of the plica- 

 tions, the last two or three having but a single spine each, and 

 that near the ventral margin. The posterior ribs were probably 

 also spinous. Length of a large specimen, 20 mm.; height, 20 mm.; 

 depth, 14 mm. 



This Brazilian species of Cardium resembles very much in shape 

 Cardium speciosum, M. and H. from the cretaceous at the mouth of 

 the Judith river, upper Missouri, but in ornamentation the two 

 differ. In C. speciosum the costa; are narrower and the spines much 

 more numerous. I have not seen the interior of the latter species. 



From the cretaceous beds at Sao Jose and Pt. Nova Cruz, Prov. 



