THE 
AMERICAN NATURALIST 
VoL. XXXII. August, 1898. No. 380. 
DENTITION OF DEVONIAN PTYCTODONTID. 
C. R. EASTMAN. 
(Continued from page 488.) 
PaLta&omyLus Woodward (1891). 
This genus at present includes the forms described by 
Newberry as Rhynchodus frangens (the type species), R. crassus, 
and R. greenei, the first two being found in the Corniferous 
limestone of Ohio, and the last-named in the Hamilton of 
Wisconsin. 
The special characteristics of this genus, as recognized by 
Woodward,! are as follows: it has a relatively very broad 
symphysial surface, a triturating oral surface, and a single 
indefinite tritoral area. From Ptyctodus it is distinguished by 
having punctate instead of laminated tritors, and the knife-edge 
of Rhynchodus is replaced in this genus by a broad, uneven, 
grinding surface. Yet the three types approximate one another 
through intimate specific gradations. For example, R, secans 
presents the same general form externally as Palæomylus, and 
between the lower dental plates of Paleomylus crassus and 
Ptyctodus ferox in the adult stage there is even greater resem- 
1 Catalogue Fossil Fishes British Museum, Pt. ii, p. 38. 1891. 
