270 
GEOLOGY OF THE FOURTH DISTRICT. 
The principal differences between this description and that of Mr. Phillips is that the mesial 
fold is not deep, and the ribs are not divaricating or duplicate toward the margin, except as 
mentioned. 
Locality —Chemung, associated with Atrypa laticostata, in great numbers. 
123. 
1. Delthyris cuspidata. 3. Delthyris mucronata 5 and 5 a. Delthyris acuminata. 
2 and 2 a. Delthyris acanthota. 4 and 4 a. Delthyris inermis. 
1. Delthyris cuspidata, n. s.— Somewhat semicircular; hinge line extended into acute 
ears ; broadly emarginate in front; mesial fold broad, moderately deep, and undefined at the 
borders; surface marked by many equal entire ribs (about 30 on each side the mesial fold), 
those on the mesial fold smaller ; ribs crossed by elevated lamellae toward the margin of the 
shell. 
It is perhaps not improbable that this fossil may be referred to some variety of Spirifera 
disjuncta. (Sowerby, Geol. Trans., New series, vol. 5, pi. 54, figs. 12, 13; pi. 55, fig. 2. 
Phillips, Palceozoic Fossils, pi. 29, fig. 128, f, g, h, and fig. 129 ; also pi. 30, fig. 129.) 
Localities —Cayuta creek ; Chemung ; Vandemark’s creek on the Genesee river. Often 
occurring in immense numbers. 
2. Delthyris acanthota, n. s. — Semicircular ; hinge line greatly extended into long acute 
ears ; emarginate in front; mesial fold well defined, often oblique, expanded at the base, and 
marked by divaricating striae ; shell marked by about eighteen equal undivided ribs on each 
side the mesial fold, and five or six smaller ones on each wing. 
2, the upper, and 2 a, the lower valve. 
