CARBONIFEROUS FOSSILS OF IRELAND. 153 



Ateypa fallax. Sow. 



Terebratula pleurodon. P/til. (pars). — Atrypa fallax. Sow. Geol. Trans. 



Sj>. Ch. — Nearly orbicular, convex ; beaks prominent, pointed ; mesial elevation slight, undefined; sur- 

 face radiated, with about sixteen or eighteen strong, angular plaits, continuing sharp and distinct to the beak. 



This is one of the forms considered by Professor Phillips to be a variety of the A. pleurodon; it is at least 

 a distinct variety, and even as such it is convenient to have a name. Length six lines, width eight lines. 



Atrypa ferita. Von Buck. sp. 



Terebratula ferita. Von Buck. Tereb. — Terebratula ferita. Phil. Pal. Fos. 



Sp. Ch. — Longitudinally ovate, subpentagonal ; beaks narrow, pointed; surface with about seven very 

 large, angular ridges. 



This species is too distinct in its plication, to be confounded with any other. Length three lines, width 

 two and a half lines. 



Atrypa flexistria. PIul. sp. 



Terebratula flexistria. Phil. Geol. York. 



Sp. Ch. — Transversely ovate, tumid; mesial elevation very large, rounded; about nine obtuse plaits raised 

 with the front margin ; the lateral plaits arched ; beak small. 



This species differs from the A. ventilahrum in the great curvature of the lateral plaits ; also in the size of 

 its rounded mesial lobe : all the plaits are obtusely rounded. Length eight lines, width ten lines. 



Atrypa gregaria. M'Coy. (PL XXIL fig. 18). 



Sp. Ch. — Trigonal ; beak of the dorsal valve very large, produced, incurved ; dorsal valve flattened ; sides 

 abruptly roimded; a very wide, but shallow, mesial depression, slightly produced in front; ventral valve an equi- 

 lateral triangle ; all the angles rounded, very convex ; front margin raised to a broad sinus ; surface smooth. 



This curioixs species is very remarkable in form, wholly unlike any of the other Palasozoic species, ap- 

 proaching nearly in size and shape to the Terebratula Uneolata, Phil., of the Speeton clay ; it is the only true 

 Atrypa I know of, resembling in this respect several of the attached Terebratula of the more recent ibrma- 

 tions. Length seven lines, width six lines, depth three lines and a half 



Atrypa hastata. Sow. sp. 



Terebratula hastata. Sow. Min. Con. — Terebratula hastata. Phil. Geol. York. 

 Sp. Ch. — Ovato-pentagonal, depressed; front truncate, slightly emarginate, depressed; sides of the beak 

 angulated ; surface smooth ; breadth two-thirds the length, which is usually one inch. 



This fossil is very abundant. The valves are more nearly equal than is usual in species of this genus ; 

 the outline of the young shell is regularly ovate, but becomes pentagonal as it increases in size; the 

 Fig. 33. front, in young individuals, is rounded, but in old shells truncate, and somewhat wedge- 

 shaped, from the depression of the middle of the valves ; there is an obtuse keel on each side of 

 the beak of the dorsal valve. The internal supports or cardinal teeth of the ventral valve, I 

 have found to be composed of two fiat, triangular laminae, having the ventral edge convex, and 

 the dorsal edge concave ; they increase in breadth towards the anterior end, where they are 

 obliquely truncated. They arise in the usual manner, one on each side of the beak of the ventral 

 valve, diverging as they approach the front margin. They reach, in the present species, some- 

 what less than half the length of the shell (see fig. 33). Length one and three quarter inches, width one 

 inch. 



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