60 SYNOPSIS OF THE CHARACTERS OF THE 



produced, flattened, abruptly truncated at the end, wliicli is rectangular ; hinge-line equal to the width of the 

 shell ; surface transversely striated ; posterior slope striated parallel to the truncated margin, and with several 

 leaving strim parallel to the hinge-line. 



This curious little shell bears much resemblance to one of Professor Phillips' figures of the Sanguinolaria 

 sulcata, Mijnst. (not of the Geol. of York.), from which it is distinguished by the length of the hinge-line, 

 close, reo-ular striation, great convexity, and the shortness of the anterior side. The striae parallel to the hinge- 

 line, very great convexity of the anterior side, and the compressed, wedge-like form of the posterior extremity, 

 are remarkable in the present species. Length three and a half lines, width seven lines. 



Cypricardia cylindrica. M'Coy. (PL VIII. fig. 23). 



Sp. Ch. Transversely elongated, three times as wide as long, cylindrical, very convex; anterior end 



short, rounded ; posterior end obliquely truncated, obtuse ; front margin entire, without sinus, parallel with the 



dorsal margin. 



The hino-e-line is about three-fourths the length of the shell, and parallel with the front margin, which is 

 entire. Length foiu' lines, width eleven lines. 



Cypricardia modiolaris. M'Coy. (PL VIII. fig. 27). 



Sp, Ch. — Transversely oblong, diagonally gibbous; beaks very small; anterior end tumid, rounded; 

 hinge-line rather more than two-thirds the width of the shell ; posterior end angulatcd, oblique, very obtusely 

 rounded ; posterior slope very obtusely rounded ; abdominal margin slightly concave ; surface with nearly ob- 

 solete concentric wrinkles of growth. 



This species has much of the general form of the C. impressa, Sow., but the beaks are smaller, the ante- 

 rior end rounded instead of being truncated, as in that species ; the hinge-margin more elevated, and the poste- 

 rior slope and extremity more obtusely rounded; it also resembles some specimens of the PuUastra complanata, 

 Sow., but has not the narrow, beaked posterior extremity, has a much smaller anterior side, and is otherwise 

 different. Length five and a half lines, width one inch one line. 



Cypricardia oblonga. M'Cojj. (PL VIII. fig. 21). 



Sp. Ch. — Transversely oblong, three and a half times wider than long, obtusely keeled; anterior end 

 short, rounded, a shallow sinus in the front margin, hinge-line about half the width of the shell; surface smooth, 

 with a few obscure undulations at the posterior end. The hinge-line of this species in shorter than is usual in 

 this genus, which, with the very elongate figure, will distinguish the species ; from the shortness of the hinge- 

 line the posterior end is very obliquely truncated, this portion of the shell is marked by a few broad, obscure 

 undrdations. Length six lines, width one inch seven lines. 



Cypricardia quadrata. MCoy. (PL VIII. fig. 22). 



Sp. Ch. — Subquadrate, gibbous, obtusely keeled, anterior side very short; subtruncate, rounded, posterior 

 side square ; hinge-line straight, as long as the shell is wide, front with a short sinus, from which a concave 

 space extends half way to the beak ; surface with faint, rather distant, concentric stris. 



This species bears a sHght resemblance to the Cypricardia retusa of the Silurian rocks, but is easily dis- 

 tinguished by the form of the anterior side ; its quadrate, gibbous form distinguishes it from most others. 

 Length six lines, width eleven lines. 



