, NIAGARA GROUP. 
279 
640. 54. ATRYPA OBTUSIPLICATA (n. sp.). 
Pl. LVIII. Fig. 2 a - h. 
Spheroidal, or more or less gibbous; ventral valve extremely convex; beak of dorsal valve 
small, closely incurved over the ventral valve ; surface plicated ; plaits simple, rounded, about' 
18 to 20, three or four of which are depressed in the dorsal valve and projecting in front, 
filling a deep sinus in the margin of the ventral valve ; a corresponding elevation on the ventral 
valve, which reaches from the base two-thirds of the way to the beak; plications crossed by 
fine subimbricating concentric strise. 
This shell is easily distinguished from the other species of this group, by its rounded form 
and obtuse plications in the perfect shell, which are subangular in the cast. The proportion of 
the two valves is variable, the ventral one often becoming extremely convex, with the sinus 
in front greatly elevated. The number of plications varies from sixteen to twenty-two in the 
greatest extremes of size I have seen; while three, and rarely four, are depressed on the one 
valve, and four or five elevated on the opposite valve. 
Fig. 2 a, b, c. Ventral, dorsal and profile views of a specimen of the ordinary size. 
Fig. 2 d. Front view of the same. 
Fig. 2 e. Ventral view of a specimen which is more expanded at the sides. 
Fig. 2 f. Front view of a specimen where the ventral valve is much elevated, and the sinus 
very deep. 
Fig. 2 g. Ventral valve of a compressed specimen. 
Fig. 2 h. Several plications enlarged, showing the concentric strire. 
Position and locality. In the shale and lower part of the limestone at Lockport. 
641. 55. ATRYPA PLICATELLAI 
Pl. LVIII. Fig. 3 a - e; and 4 a, b. 
Terebratula {Anomites) plicatella, Linne, Wahuenberg, Dalman, Hisinger, &c. 
Terebratula lacunosa, Schlotheim, Nachtr. 1, pag. 68, pl. xx, fig. 6. 
— — Sowerby ; Murchison, Sil. System, pag. 624, pl. 12, fig. 10. 
Not T. lacunosa, Dalman and Hisinger. 
Obovate, outline subtriangular ; surface strongly plicated; plications simple, acute, crossed 
by prominent threadlike strise ; beak of the dorsal valve sharp, slightly extended, and scarcely 
incurved; three or four plications on the dorsal valve depressed, and strongly elevated in 
front; an equal number of plications on each side of the mesial sinus and elevation. 
This species differs from the preceding in the more angular form of the shell, the extended 
sharp beak of the dorsal valve, and in the sharp prominent strise, which contrast in a very de¬ 
cided manner with the rounded strise and closely incurved beak of A. obtusiplicata. The figure 
of T. lacunosa (Sowerby), from the Wenlock limestone, bears a close resemblance to our fossil. 
