278 
PALAEONTOLOGY OF NEW-YORK. 
This very peculiar little shell is easily recognized from the great disparity of the valves, the 
ventral one being always quite plane or concave, while the dorsal one is extremely convex. 
The number of plications is variable, and there is sometimes a tendency to bifurcation or inter- 
plication among the lateral ones. There is, in the Delthyris shaly limestone, a species very 
similar to this one, but it is a stronger shell. There is likewise in that rock another species of 
similar form, but with finer plications or striae. 
Fig. 6 a, b. A young individual, with scarcely two defined plications on each side of the centre. 
Fig. 6 c, d. Ventral and dorsal valves of a specimen, with three plications on each side of the 
central pair. 
Fig. 6 e. Another specimen having four plications. 
Fig. 6 f. Profile view of a full grown individual. 
Fig. 6 g. Front view of a specimen. 
Fig. 6 i, k. The interior of a dorsal valve, and the same enlarged, showing the perforation of 
the apex extending to the cardinal line. 
Fig. 6 l, m. The interior of the ventral valve, and the same enlarged. 
Position and locality. In the shale at Wolcott, Wayne county. 
639. 53. ATRYPA BREVIROSTRIS(I). 
Pl. LVIII. Fig. 1 a 
Compare. Terebratula brevirostris, Sowerby in Murchison’s Sil. System, pag. 631, pl. 13, 
fig. 15. 
Also T. interplicata, Idem, pag. 631, pl. 13, fig. 23. 
And A . interplicata, pag. 275, pl. 56, fig. 2, of this volume. 
Transversely elliptical or ovoid, gibbous ; ventral valve more convex than the dorsal; beaks 
short, nearly equal; surface plicated ; plications 20 to 24, sharp, bifurcating or interplicated ; 
five or six of the plications depressed in the dorsal valve, and a corresponding number elevated 
in the ventral valve; concentrically striated. 
This shell is closely allied to A. interplicata , and perhaps only a variety of that species, 
though it corresponds with the description of T. brevirostris ut supra. The sinus is broader 
and less deep than the ordinary specimens of A. interplicata , and I have not been able to find 
a succession of forms connecting those of that species figured with the present one, which 
nevertheless possesses many similar features. 
Fig. 1 a, b. Ventral and dorsal views of a specimen. 
Fig. 1 c. Profile view of the same. 
Fig. 1 d. Cardinal view. 
Fig. 1 e. Front view. 
Fig. 1 /. An enlargement of the plications, showing concentric striae. 
Position and locality. In the shale at Lockport. 
