OF DENISON UNIVERSITY. 
91 
GENUS EICHWALDIA, Billings. 
XVIII. Eichwaldia reticulata^ Hall. 
{Plate XIII, Figs. ^ a, b.) 
Shell broadly triangular ovate, gibbous, cardinal slopes flattened. 
Ventral beak small, acute, flattened on the back, closely incurved, 
the sinus extending from the beak to the anterior edge, broad, distinct. 
Dorsal valve more convex, beak obtuse, strongly incurved, a low, 
fairly defined mesial fold extending from the beak to the anterior 
margin. 
Surface covered by fine, hexagonal, reticulate markings, largest 
along the antero-lateral slopes, and decreasing in size towards the sinus 
and posterior regions. A small space near the ventral beak is destitute 
of markings. 
Length, 8 mm.; breadth, 8 mm.; convexity, 6 mm. 
Locality and position. Fauvers’ Quarry north of Dayton, Clinton 
Group. Collection of Mr. E. M. Thresher. 
Lamellibranchiata. 
I. Pterinea brisa, _ . . - Hall. 
II. Grammysia Caswelli, _ _ _ n. sp. 
III. Cypricardites ferrugineum - Hall and Whitfield. 
IV. Nucula minima, - - - - - n. sp. 
The Lamellibranchiata of the Clinton Group of Ohio are but few 
both in the number of species and in the frequency of their occurrence. 
Pterinea brisa, if correctly identified, adds another link connecting 
this formation with the Niagara Group of the West. It occurs also at 
Waldron, Indiana, and Bridgeport, Illinois. 
GENUS PTERINEA, Goldfuss. 
I. Pterinea brisa. Hall. 
{Plate XIII. Figs. 14 <2, b.) 
Left valve alone found. Body of the shell obliquely sub-ovate, 
extremely inequilateral ; anterior wing moderately extended ; sinuate 
at its junction with the body ; posterior wing acutely extended a little 
beyond the posterior extremity of the shell ; umbo prominent, beak 
rising a little above the hinge line, muscular impression in right valve 
unknown from want of specimens. 
