FISHES OF THE DEVONIAN AGE. 57 
running off to a pointed edge, where it was overlain by the articular portion 
of the mandible. 
The upper margin of the dentary bone is thickly set with conical, 
pointed teeth. Embraced within the anterior extremities of the mandibles 
is an arch of bone, which supports a series of large, conical, sigmoidally 
curved teeth, seven or eight in number, set vertically, and projecting down- 
ward, forward, and upward. ‘These teeth show several prominent roots, 
which partially embrace the bases of the adjacent teeth. The exterior sur- 
faces of the cephalic plates and the exposed portions of the maxillaries and 
mandibles are thickly set with small enameled tubercles, which have the form 
of appressed, striated, or sulcated cones. The body was covered with 
relatively thin, highly ornamented scales. These have a circular or ellip- 
tical outline; the under surface is smooth, or faintly marked with concen- 
tric lines, and often bears a central elevated tubercle or ridge. The exterior 
surface shows an anterior semi-lunar space, occupying about half its area, 
where adjacent scales were superimposed This space is comparatively 
smooth, but is delicately ornamented with radiating lines of pits. The pos- 
terior and exposed portion of each scale is roughened with appressed, striated 
tubercles, similar to those on the cephalic plates, and with branching, some- 
what foliated ridges of enamel. 
Formation and locality: Corniferous limestone; Columbus, Delaware, 
and Sandusky, Ohio. 
Section B.—FisHes oF THE HamILTon GRovp. 
In the State of New York the Hamilton group consists mainly of 
shales—argillaceous and bituminous—with only two thin bands of lime- 
stone, never over three feet in thickness in a thousand feet of strata. As 
we go westward and recede from the old shore the sheet of land-wash 
becomes thinner, the sandstones and clay shales of New York disappear, 
while the bituminous shales are more constant, running together and form- 
ing a mass, which in Ohio and further south is a very striking feature in the 
geology. I have called this in Ohio the Huron shale, because it forms for 
a long distance the banks of the Huron River, and as it represents several 
distinct strata in New York and Pennsylvania, it could not with propriety 
