152 PALEOZOIC FISHES OF NORTH AMERICA. 
that it is impossible to say whether it carried denticles or a cutting edge. 
The anterior extremity formed an acute and polished tooth, bearing a carina 
along its anterior border; below, the mandible is uniformly arched and 
terminates in a rather sharp edge; outside it is peculiarly corrugated and 
roughened. On the inside it shows the same rough bony surface, with a 
furrow parallel to the lower margin. The posterior extremity, where broken 
off, is quite narrow and thick, and it is evident that the fracture was just 
along the line between the exposed and covered portions. No evidence is 
given by an internal ridge of the presence of a second point on the upper 
margin, but a small denticle may have existed there where the margin is 
broken away. This mandible differs from all others known to me by its 
narrowness, the roughness of the surface, and the similarity and simplicity 
of the inner and outer surfaces. 
Formation and locality: Cleveland shale; Black River, Lorain County, 
Ohio. Collected by Mr. Jay Terrell. 
DINICcHTHYS INTERMEDIUS, 0. Sp. 
Plate X, Figs. 1,2; Plate XLVI, Figs. 1-42; Plates LI, LII. 
Cranium fifteen inches in length and width ; mandibles having the gen- 
eral forms of those of D. Terrelli, but smaller—fifteen or sixteen inches in 
length; posterior portion of cutting edge of dentary bone set with com- 
pressed, lancet-shaped denticles; maxillaries about four inches long by two 
inches wide, strongly arched vertically, and like the dental plates of the 
under jaw carrying denticles on the posterior margin; premaxillaries appar- 
ently similar to those of D. Terrelli, but much smaller; suborbital plates 
relatively short, the expanded portion being in some cases nearly square 
and about four inches long and broad; eyes about three inches in diameter. 
The dorsal shield and supra-scapulas are rounder in outline than those of 
D. Terrelli and, like the other parts mentioned, are about half as large. Of 
the plastron the anterior lateral plate is shorter and relatively broader than 
in the larger species, the posterior ventral plate oblong in outline, about as 
large as the anterior plate, but thinner. 
Some years ago a mandible of Dinichthys of medium size was found by 
Mr. Jay Terrell in Lorain County, Ohio, which, with the general form and 
