64 SYNOPSIS OF THE CHARACTERS OF THE 



nearly straight ; surface nearly smooth, marked towards the margin with fine, transverse lines of growth. Length 

 four lines, width six lines. 



Axmus OBLiQUTJS. M'Coy. (PI. VIII. fig. 29). 



Sp. Ch. Obliquely ovate, convex ; beaks large, prominent, close to the anterior end ; anterior side very 



short, rounded, front margin convex ; posterior side lengthened, very obliquely truncated ; a strong ridge from 

 the beak to the posterior angle ; surface smooth, except on the short, anterior side, which is marked with fine, 

 rather distant, transverse strife ; epidermis produced into long fringes beyond the margin. 



This species occurs in company with the A. depressa. A. axiniformis, and A. carhonaria, Portk., from all of 

 which it is distinguished by its great obliquity, and the inequality of its sides ; the transverse striae also appear 

 hmited to the anterior side in the present shell. Length seven Unes, width eight lines. 



AxiNus OBOVATUS. Bl'Coy. (PL VIII. fig. 30). 



Sp. Ch. — Transversely obovate, depressed; beaks large, not prominent, close to the anterior end, which is 

 broadly rounded ; abdominal margin convex, posterior end pointed, equally rounded towards the dorsal and 

 ventral margins ; surface smooth, or with a few irregular, concentric striae. 



The principal feature in this regularly obovate shell, is the great and equal convexity of the dorsal and 

 ventral margins as they approach the posterior end, which is thus regularly pointed ; the ridge separating the 

 posterior slope from the body of the shell is very shghtly defined. This shell is almost identical in form with 

 the Lyrodon ovatum of the muschelkalk. Length nine lines, width one inch five fines. 



AsiNus ORBICULARIS. M'Coy. (PI. VIIL fig. 28). 



Sp. Ch. — Orbicular, length and width equal, depressed, smooth; beaks small, nearly central ; a slightly 

 marked, rounded, oblique ridge on each side of the beak, that on the posterior side strongest ; anterior and pos- 

 terior margins almost equally convex. 



This little shell is distinguished from all the allied species by its nearly central beaks and orbicular outline, 

 and from the A. carhonaria. Port., by the height of the sides and their more perfectly rounded form. 



Length three and a half lines, width four lines. 



DoLABRA. M' Coy. 



Gen. Ch. — Subrhomboidal, gibbous, slightly inequivalve, inequilateral, anterior side rounded, posterior 

 side subtruneate, generally oblique ; shell thick, beaks large, prominent ; in the left valve two long, diverging, 

 cardinal teeth, anterior one longest, and two lengthened, posterior, lateral teeth. 



I have found it necessary to frame this genus for the reception of a considerable number of shells of the 

 Palajozoic rocks, hitherto classed with Lyrodon, Cucidlaa, Cypricardia, &c. Some few shells of this group 

 are placed by Goldfuss in the genus Lyrodon, although it is obvious, even from their external form, that they 

 can have no affinity with the TrigonicB of the Oolites ; besides which, those last are equivalved, and have 

 strongly sulcated, cardinal teeth, while the DolahrcB are ineqiuvalve, and have simple cardinal teeth : from the 

 Cypricardm they differ in general form, being inequivalve, and in their long diverging cardinal teeth. All the 

 Devonian Cucullcea's of Marwood belong to this group, the long, anterior, cardinal teeth having been taken 

 for the prominent edge of the muscular impression, although, as Professor Philhps has observed, it is on the 

 wrong side of the beak for Cuctdlaa; the lateral teeth oi Cucidhea, anijusta as figured by Mr. Sowerby, or as 

 I have observed them myself in Lish specimens, do not seem to correspond to those of Cucullaa. 



