No. 379. ] DEVONIAN PTYCTODONTIDAZE. 485 
principally in the configuration of the symphysial area, a tran- 
sitional stage between Ptyctodus and the next following genus. 
Ruyncuopus, Newberry (1873). 
(1) R. secans. — This species, which is the type of the genus, 
is not uncommon in the Corniferous Limestone of Ohio, and 
is interesting for having furnished a group of four teeth pre- 
served in natural association. There is but little difference in 
the form of upper and lower dental plates, and both terminate 
anteriorly in prominent beaks. It is probable that the latter 
character is not merely specific but generic, as R. excavatus 
also has sharp beak-like projections in both jaws. An inden- 
tation occurs just back of the beak in the upper jaw where 
the terminal point of the lower came in contact with it, thus 
proving that the upper jaw protruded forward in advance of 
the lower, as in Ptyctodus. The lower dental plate is deeper 
than the upper, which was limited vertically by the cranial 
wall, and its triturating surface is frequently more uneven. 
Its inner face is beveled away through contact with the upper 
jaw, the two working together like blades of shears. 
A knowledge of this latter character compels us to dissent 
from Newberry’s determination of one of his figures! as a “ left 
maxillary tooth ” in spite of its having a nearly straight cutting 
edge. Owing to the fact that it is beveled on the inner face 
and is not cut away behind the anterior beak we prefer to 
regard it as the right lower dental plate. 
(2) R. occidentalis. — This species has never been figured, 
and the writer has been unable to obtain examples of it. New- 
berry’s original description is as follows?: “ Teeth of small size, 
much compressed. Anterior margin slightly curved, but nearly 
vertical. Superior margin gently arched downward from the 
prominent anterior point, forming a much-compressed triturat- 
ing surface or edge. Posterior portion of upper margin acute- 
edged. Exterior lateral surface striated obliquely backward. 
1 Newberry, J. S. Rep. Geol. Surv. Ohio, vol. i, Pt. ii (Paleontology), Pl. 
XXVIII, Fig. 1 (1873). Also figured in Mon. U.S. Geol. Surv., vol. xvi (1889), 
Same number of plate and figure. 
? Annals N.Y. Acad. Science, vol. i (1878), p. 192. 
