CLINTON GHOtfP. 
71 
Fig. 6 a, b. Ventral and profile view of a small specimen. 
Fig. 5 c, d, e. Dorsal valves of three individuals of different size* 
Position and locality. In the arenaceous layers near the base of the group in Oneida county, 
Blackstone’s quarries. {State Collection.) 
458. 29. ATRYPA EMACERATA. 
Pl. XXIII. Fig. 6 a> b, c, d. 
Flabelliform, subrhomboidal, trilobate; surface plicated ; plications about eighteen, six of 
them raised in front on the mesial lobe, usually bifurcating equally, those on the mesial lobe 
often'having a smaller one intercalated ; concentrically marked by undulating imbricating 
lamellae. 
This species is known only in the,green shales of Sodus and Rochester. All the specimens 
seen are flattened, and the shell partially or entirely destroyed. In the specimens figured, 
although the ribs are distinctly preserved over the entire surface, the outline and extent of the 
muscular impression are clearly perceptible. On the sides of the shell, the ribs are distinctly 
and equally bifurcating above the centre, and often near the beak j on the mesial lobe, in ad¬ 
dition to this, there are other smaller ribs intercalated. 
Fig. 6 a, l. Two individuals of this species in green shale. 
Fig. 6 c. The surface enlarged,'showing the concentric striae. 
Fig. 6 d. A cast of the beak of the same. 
Position and locality. In the upper green shale at Sodus, associated with Leptcena corrugata 
and Spirifer radiatus ; and in the same position at Rochester and intermediate localities. 
459. 30. ATRYPA ROBUSTA. 
Pl. XXIII. Fig. 7 a, b, c, d. 
Subrhomboidal, trilobate; surface marked by eleven or twelve strong angular plications on 
each valve, four of which are raised on the mesial fold, and three in the depression of the op¬ 
posite valve ; plications crossed by abruptly undulating striae ; cardinal line not extended, and 
the sides sloping abruptly from the beak. 
The specimen figured is somewhat compressed, the perfect form being more rotund. The 
species is readily distinguished by the small number of strong angular plications, which are 
undivided from the beak. In the specimen figured, the beak of the dorsal valve is broken off 
at the termination of the beak of the ventral valve; beyond which it extended some distance, 
as usual in species of this form. The concentric striae in the specimen figured are nearly ob¬ 
literated by exfoliation of the shell. 
