172 
GEOLOGY OF THE FOURTH DISTRICT. 
line slightly arched, extending beyond the width of the shell, and obtusely angulated. The 
surface is marked by a few concentric lines of growth. 
See also a figure of the same shell in the Hamilton Group. 
Locality —Vienna, Ontario county. 
5. Delthyris duodenaria, n. s. — General figure semicircular; valves nearly equally con¬ 
vex : mesial fold much elevated towards the front; ribs 12, gradually decreasing in size from 
the centre, rounded, and crossed by concentric undulating lines. 
The specimen is imperfect, and though the fossil is abundant, I have never been able to 
obtain a perfect one. It is readily known by the number of its ribs and the undulating lines. 
Resembles D. raricosta of Conrad, the D. undulatus of Vanuxem (Report, p. 132), but differs 
from that in form and in the number of ribs. Concentric lines often obsolete. 
Locality —Five miles east of Buffalo, and at other points on the Macadam road. 
6. Pleurorhyncus trigonalis, n. s. — Sub-triangular ; beaks little elevated ; surface marked 
by about 20 ribs, some of which are divided ; anterior surface broadly cordate; posteriorly 
slightly elevated and conoidal. 
2 a. A view of the base, showing a portion of the shell remaining, which extends anteriorly 
beyond the cast, and is striated. This appears like a kind of sheath, which has apparently 
no opening upon the base. 
This shell is certainly unlike the P. cuneus of the Schoharie grit. 
Locality —Williamsville, Erie county. 
68 . 
1 Pterinea cardiiformia. 
2. Tentaculites scalaria. 
3. Orthonychia. 
4. Euomphalus? rotundus. 
5. Calymene crassimarginata. 
6. Acroculia erecta. 
