CARBONIFEROUS FOSSILS OF IRELAND. 61 



Cypricardia RHOMBEA. Pllil. 



Cypricardia rhombca. Phil. Geol. York. 



I have only seen imperfect fragments of this shell ; it is transversely oblong, with a very strong, diagonal 

 keel ; the dorsal and ventral margins parallel ; posterior extremity truncated nearly at right angles with the 

 hinge-line, which latter is nearly as long as the shell is wide. 



Cypricardia sinuata. M'Coy. (PI. VIII. fig. 26). 



Sp. Ch. — Transversely ovate, obtusely keeled, anterior end very small, rounded, a distinct sinus in the 

 ventral margin, surface smooth ; width less than three times the length ; hinge line two-thirds the width of 

 the shell. 



This species is allied to the Cypricardia ohloiifja, but is much less transverse, has a longer hinge, larger 

 abdominal sinus, and more obtuse posterior end ; there are a few obscure concentric undulations visible towards 

 the posterior end. Length five lines, width one inch three lines. 



Cypricardia socialis. M'Coy. (PI. VIII. fig. 12). 



Sp. Ch. — T\vice and a half as wide as long, gibbous; dorsal and ventral margins parallel ; beaks prominent, 

 close to the anterior end ; anterior side short, rounded, separated from the body of the shell by a deep sinus in 

 the front margin, from which a broad, shallow sulcus extends obliquely to the beak ; posterior end obHquely 

 subtruncate, rounded ; surface marked with strong, irregular, transverse striae. Length four lines, width nine 

 lines. 



Cypricardia TUMiDA. M'Coy. (PL VIIL fig. 13). 



Sp. Ch. — Transversely ovate, gibbous, length two-thirds the width, smooth; beaks very large, tumid, close 

 to the anterior end ; anterior side short, rounded ; posterior end rounded, not distinguished from the body of 

 the shell. 



This little species has much the aspect of the C. semicidcata, but is less wide, the posterior end much broader, 

 and the surface is entirely devoid of transverse sulci, neither is there any furrow from the beak to the front 

 margin. Its great convexity, shortness, and smooth surface, distinguish it from any of the allied species. 

 Length four lines, width five lines and a half 



Sedgwickia. M'Coy. 



Gen. CA.— Equivalved, or nearly so, inequilateral; shell very thin, inflated ; dorsal and ventral margins 

 subparallel ; anterior half of each valve marked with strong, transverse ridges ; posterior half smooth ; beaks 

 moderate ; anterior side very short, round ; posterior side broad, lengthened, subtruncate. 



The genus Sedgieickia (M'Coy) is composed of a very elegant little group of shells, having analogies which 

 place them, as it were, between the so-called Cypricardia of the older strata, the Axini (Sow.), and the Lep- 

 todomi (M'Coy). The passage to Cypricardia is marked by such shells as the Sedgwickia minima, M'Coy, 

 and S. corrm/afa, M'Coy, while an approach to the same form is indicated by such species oi Axinus as the 

 A. ohovata (M'Coy), and the A. ohliqua (M'Coy), which, however, still retain the oblique, acutely angular pos- 

 terior side, and very short, oblique, hinge-line oi Axinus, and wliich distinguishes them at a glance from the true 

 Sedgwickia's, all of which have a broad, subtruncate, posterior end, and a hinge-line nearly as long as the shell. 

 They are entirely without hinge teeth, their hinge resembling that of Thraciu. 



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