PTYCTODONTIDiE. 
37 
■under each tooth 1 is conclusive proof of their bearing no relation to 
the familiar membrane-bones thus named in higher fishes. 
Synopsis of Families . 
I. [Imperfectly defined. Spines unknown.] 
One pair of dental plates above and 
below . Ptyctodontidje (p. 37). 
II. Dorsal fin-spines absent. Rostral spine 
in male. 
Trunk depressed, snout elongated. Two 
pairs of dental plates above, one pair 
below . Squaloraied^: (p. 40). 
III. Spine in front of anterior dorsal fin. 
Rostral spine in male. 
Few dermal plates on head. Two pairs of 
dental plates above, one pair and an 
anterior azygous tooth below . Myriacanthid^e (p. 43). 
No dermal plates. Two pairs of dental 
plates above, one pair below. Celqueridje (p. 52). 
Family PTYCTODONTIDiE. 
A family at present indefinable, of doubtful ordinal position, 
known only by remains of the dentition. A single pair of large, 
laterally compressed, dental plates in each jaw, meeting at the 
symphysis and with few tritoral areas. 
The genera of this familv have not hitherto been defined, even so 
far as existing materials will permit. There are as yet no examples 
of the teeth in the collection of the British Museum ; but an exami¬ 
nation of a large number of Russian specimens in St. Petersburg, 
American specimens in New York, recently discovered examples 
from Canada in the Geological Survey Collection at Ottawa, and 
several undescribed forms from the Eifel Devonian in the Museum 
of Comparative Zoology, Cambridge (Mass.), has suggested to the 
writer the following provisional arrangement. 
Synopsis of Genera . 
I. Symphysial surface narrow; tritors more or 
less laminated. 
Oral surface triturating, the tritors being 
well differentiated and consisting of 
hard, punctate, superimposed laminae, 
arranged obliquely to the functional 
surface . Ptyctoclus , Pander. 
1 R. Owen, Odontography, p. 65. 
