EASTMAN : CAKBONIFEEOUS SHARKS. 57 



teeth are displayed by numerous diverse forms, such as Protodus, Gloss- 

 odus, Sandalodus, CochUodus, Periplectrodus, Ouychodus and other Palsje- 

 ozoic fishes. Amongst these the type-specimen of " Belodus coxanus " 

 Newberry, which is in reahty the symphysial series of CochUodus latus, 

 exhibits only a slight inrollment, and is hence indicative of a pi-imitive 

 stage. A more advanced stage is represented in another family by the 

 correspoiading series of Campodus variabilis and the various species of 

 Edestus. Campyloprion, as the name indicates, is a more arcuate form 

 and possesses more immerous 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 aftorded 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 I'emote a period as the Devonian of offshoots 

 from the primitive Elasmobranch stem, which approximated the 

 modern ray type in certain notable respects. That such earlj' approxi- 



1 Lohest, M., Recherches sur les poissoiis des terrains paleozoiques de Belgique. 

 Ann. Soc. Ge'ol. Belg., Vol. XI., p. 314, 1883. 



2 St. John, O., and Worthen, A. /i., Pal. lUinois, Vol. VI., p. 318, PI. VIII., 1875. 



