22 On Lingulasma^ Etc. — Ulrich. 
valve a little convex instead of concave. The species is dis- 
tinguishable from all others known to me by the extreme thin- 
ness of its shell. 
Formation and locality: Lowest beds of the Cincinnati 
group, a few miles south of Covington, Ky. Collections of 
Mr. C. Schuchert and the author. 
TREMATIS ORASSIPTJNCTA.n. sp. 
Fig. 7-7 a. 
Shell nearly circular, 15.5 mm. wide and 16 mm. long. 
Upper or dorsal valve moderately and uniformly convex, 
most elevated in the posterior half; beak very small, pointed, 
not elevated, and scarcely projecting beyond the margin. 
Surface with straight or zigzag radiating lines increasing by 
interpolation or bifurcation ; the interspaces between them 
grow wider toward the front and lateral margins where from 
twelve to sixteen occur in 5 mm. The concave interspaces be- 
tween them are not equal, some being considerably wider than 
the average with only three in 2 mm. The radiating lines are 
connected by cross ridges of which from twelve to fourteen 
occur in 5 mm., measuring from the margin. These lines 
form a rather coarse reticulation with meshes of quadrate, pen- 
tagonal or hexagonal form. In addition there are undula- 
tions of growth and very fine and crowded concentric lines. 
The latter, however, do not appear to have crossed the radiat- 
ing striie, having been noticed at the bottom of the depressed 
spaces. 
Lower valve unknown. 
At first I was disposed to regard this species as being iden- 
tical with the 2'. ottaioaensis of Billings. Since seeing the 
types of that beautiful species and collecting fine examples of 
it not only at the original locality, but also from the middle 
Trenton beds of Kentucky, I have come to the conclusion 
that the Ohio shell belongs to a distinct class. T. ottawaen- 
sis is a larger shell, slighter, Avider and its surface reticulation 
finer. The average number of meshes in 5 mm. is nearly con- 
stantly twenty-five or twenty-six against twelve to sixteen in 
T. crassipuncta. The umbones of the upper valve of the 
latter is also less prominent and its beak more pointed and 
smaller. 
Formation and locality : From shales of the middle beds 
of the Cincinnati group near the tops of the hills at Cincin- 
