132 
SEIACHII. 
The following extinct genera, being known only by the dentition 
and vertebrae, are provisionally associated with the family of Mylio- 
batidae. Apocopodon has already been placed here by Cope, and 
the present writer 1 2 has suggested that this genus is not improbably 
a link between the more typical members of the family and the 
Cretaceous Ptychodus. 
Genus APOCOPODON, Cope. 
[Proc. Amer. Phil. Soc. vol. xxiii. 1886, p. 2.] 
Median teeth quadrate in form; side teeth with irregularly an- 
gulated lateral extremities. Crown elevated, separated from the 
root by a constriction, the grinding surface covered by a dense layer, 
with fine antero-posterior wrinkles ; attached surface of root with 
few, very shallow grooves. 
Apocopodon sericeus , Cope, loc.cit., is the only known species, from 
the uppermost Cretaceous of Maria Farinha, Province of Pernam¬ 
buco, Brazil. I . j : , A ' ” 
Genus PTYCHODUS,4gassiz.^V V fry*' ^^ 
[Poiss. Foss. vol. iii. 1839, p. 150 1 ^ ^ u 
Syn. Aidodus,' F. Dixon, Foss. Suss. 1850, p. 366. 
»\ 
Teeth quadrate in form, with elevated crown, somewhat over¬ 
hanging, and sharply separated from the root by a constriction. 
The crown is enamelled and ornamented with large transverse or 
radiating ridges, surrounded by a more finely-marked marginal area, 
of greater or less extent. The surface of attachment of the root is 
smooth. 
Fig. 6. 
Diagram of arrangement of teeth of Ptychodus decurrens 2 . 
A. Upper jaw. B. Lower jaw. 
1 Proc. Geol. Assoc, vol. x. (1888), p. 297. 
2 Reduced from Proc. Geol. Assoc, vol. x. (1888), p. 296. 
