OF DENISON UNIVERSITY. 
33 
strong very nodose radii separated by a shallow groove and one, 
or occasionally two, unornamented ridges. 
Our specimens are all imperfect, but a nearly complete right valve 
indicates that the outline must agree closely with that of L, interradia- 
tus, H. from the Hamilton group, with which it agrees in size. The 
surface structure serves to distinguish it from other members of the 
genus. Height, 37 mm., length, 43 mm. 
Concretionary zone about seventy feet below conglomerate I, in 
Licking and Richland counties. 
PTERINOPECTEN CARINIFERUS. Her. 
(Plate V, Fig. 12.) 
Additional specimens show that the form of the left valve is in- 
constant in one particular. The anterior ear occasionally does not 
correspond to its fellow in outline but is continued from the anterior 
extremity of the hinge nearly at a right angle to point of union with 
the body. The ear therefore is nearly a right-angled triangle, but is 
marked by the impression of the margin of the corresponding ear of 
the right valve. This must be regarded as the typical form, but is 
rarely seen as in most left valves the byssal sinus is well-marked. 
Length, 17 mm., height, 14 mm., distance between radiating striae 
nearly i mm. 
This species is quite abundant in Ashland Co. , about seventy feet 
below conglomerate I, and also occurs at Lodi in the concretions at 
the very base of the exposure. 
PTERINOPECTEN (?) ASHLANDENSIS. Sp. n. 
(Plate XI, Fig. 4.) 
Known only from fragments of the left valve. Shell triangularly 
sub-elliptical in outline, somewhat oblique, length somewhat greater 
than the height. Umbonal region narrow, acute, depressed, body 
rapidly expanding toward the front, ant-umbonal margin concave, 
long ; anterior ear unknown ; front margin a gentle curve ; post-um- 
bonal margin straight ; posterior ear small, flat, obtusely triangular. Sur- 
face depressed convex, ornamented by about fifty irregular wavy ribs 
in pairs, separated by narrow impressed grooves, which are crossed by 
