FISHES OF THE DEVONIAN AGE. 45 
ASTEROSTEUS STENOCEPHALUS, Newb. 
Plate XXX, Fig 1. 
Asterosteus stenocephalus, N.; Paleontology of Ohio, vol. 2, p. 33, pl. 54, fig. 1. 
Head eight inches or more in length, by two and a half in width, ex- 
cept at the occiput, where it suddenly widens and becomes four or five 
inches broad. It terminates posteriorly in two excavated arches, of which 
the surface is roughened, apparently for muscular attachment. Projecting 
behind and below these arches are two bony condyloid prominences an 
inch or more in length’ The upper surface of the cranium is somewhat 
irregularly covered with stellate tubercles, which vary in size from one- 
eighth to one-twentieth of an inch in diameter. The sides of the cranium 
are somewhat beveled and roughened, and are traversed by an irregular 
line of relatively large tubercles. Near the anterior end the head seems to 
be suddenly narrowed, and just at this point it bears two deeply impressed, 
elliptical nasal (?) orifices, placed side by side, somewhat divergent for- 
ward, and having a length of five lines and a breadth of two lines. The 
dentition is entirely unknown, as is also the covering of the body. 
Formation and locality: Corniferous limestone; Sandusky and Dela- 
ware, Ohio. 
Order HOLOCEPHALI. 
Genus RHYNCHODUS, Newb. 
In the Paleontology of Ohio (vol. 1, p. 307) I described a peculiar 
group of dental organs of Elasmobranch fishes, under the name of Rhyn- 
chodus. ‘These occur not infrequently in the Corniferous and Hamilton 
limestones, but had not before attracted attention, simply because no one 
had interested himself in the vertebrate fossils of American Devonian rocks. 
The following is a brief generic description of these fossils : : 
Teeth somewhat crescent-shaped or semi-circular, much compressed ; 
the exterior margins regularly curved, the interior nearly straight and more 
or less thickened; one of the cornua produced and somewhat acute, the 
other rounded and obtuse. The straight side formed a triturating or cutting 
edge. In some species it was sharp, and played upon the similar edge of 
