FISHES OF THE DEVONIAN AGE. 51 
one on the middle of the exterior margin and one near the anterior ex- 
tremity. The inner surface of the tooth shows a prominent ridge running 
up to the anterior point. 
This tooth is evidently fitted for triturating rather than cutting, and 
resembles in its general form Lt. frangens, of the Corniferous limestone. It 
is, however, much smaller and thinner; and the tubercles of the upper sur- 
face are situated differently from those in that species. 
Formation and locality: Hamilton group: Brown Deer, Milwaukee 
County, Wis. Collected by Prof. T. C. Chamberlin. 
RiyNCHODUS GREENEI, n. sp. 
Teeth large and massive, six inches in length, one inch in thickness at 
the anterior border; elliptical or semi-circular in outline, the anterior angle 
produced into a strong triangular point; posterior to this a triturating flat- 
tened surface extends to or beyond the middle of the superior margin. 
This surface is broadest anteriorly, where it is three-quarters of an inch in 
width, and bears two obtuse rounded tubercles. The sides are smooth and 
polished, terminating below in sharp, somewhat waved, edges. 
The teeth of this species resemble those of Rhynchodus frangens, from 
the Devonian rocks of Ohio, but are narrower vertically, and are longer 
and much thicker at the anterior border. 
Formation and locality : Hydraulic limestone of Hamilton age; Milwau- 
kee, Wis. Collected by Mr. Thomas A. Greene. 
Order PLACODERMI. 
DINICHTHYS PRECURSOR, 0. sp. 
Plate XLI. 
In the Corniferous limestone at Sylvania, Ohio, Mr. G. K. Gilbert, 
when connected with the Ohio Geological Survey, obtained a dorsomedian 
plate of what seems to have been a species of Dinichthys. It is about eight 
inches long by five inches broad; the sides nearly straight, the anterior 
border emarginate. The plate was transversely arched, nearly straight 
along its central line; the external surface in parts smooth or finely pitted, 
