EASTMAN: CARBONIFEROUS SHARKS. 57 
teeth are displayed by numerous diverse forms, such as Protodus, Gloss- 
odus, Sandalodus, Cochliodus, Periplectrodus, Onychodus and other Pale- 
ozoic fishes. Amongst these the type-specimen of “ Helodus coxanus ” 
Newberry, which is in reality the symphysial series of Cochliodus latus, 
exhibits only a slight inrollment, and is hence indicative of a primitive 
stage. A more advanced stage is represented in another family by the 
corresponding series of Campodus variabilis and the various species of 
Edestus. Campyloprion, as the name indicates, is a more arcuate form 
and possesses more numerous segments ; and finally, in the completely 
coiled Helicoprion, we observe the most extreme specialization in this 
direction. 
Campodus. 
(Plates 1-3.) 
The best account of the dentition of this genus is that given by Max 
Lohest * in 1883, who pointed out the close similarity between it and 
the living Cestracion (Heterodontus), and corrected certain errors in the 
earlier restorations of St. John and Worthen.? The observations of all 
these writers were based upon a unique specimen from the Missourian 
of Osage County, Kansas, referred by them to the left ramus of the lower 
jaw, and comprising upward of 450 teeth arranged in eighteen transverse 
rows. This specimen was deficient at its anterior extremity, where the 
individual teeth are greatly diminished in size: and no information 
was afforded respecting the nature of the union of this ramus with its 
fellow, or the presence or absence of symphysial teeth. The gape of 
the mouth being thus entirely conjectural, the jaws were restored by St. 
John and Worthen after the fashion of Raja, with the forward ends 
apposed to one.another in a nearly straight line; and inferentially the 
structure of Campodus was supposed by them to have conformed to 
the type of modern rays. 
Were there a reasonable basis for this view, it would be of some mo- 
ment in considering the question of the origin of rays. For although 
the Batoid type is regarded as a comparatively modern derivative, not 
antedating the Jurassic’ so far as known, nevertheless we cannot deny 
the existence at even so remote a period as the Devonian of offshoots 
from the primitive Elasmobranch stem, which approximated the 
modern ray type in certain notable respects. That such early approxi- 
1 Lohest, M., Recherches sur les poissons des terrains paléozoiques de Belgique. 
Ann. Soc. Géol. Belg., Vol. XI., p. 314, 1883. 
2 St. John, O., and Worthen, A. H., Pal. Illinois, Vol. VI., p. 218, Pl. VIII., 1875. 
