EASTMAN: CARBONIFEROUS SHARKS. 61 



Now, with respect to inrollment or coiliug, we need only repeat that 

 this character pervades numerous sharks, both those with piercing and 

 those with crusliing teeth. Indeed, some forms are known, such as 

 CochHodus, Psephodus, etc., which have posterior dental plates adapted 

 for crushing, and feebly prehensile symphysial teeth (e. g., " Helodus 

 coxanus " Newberry). In Campodus the anterior series are only mod- 

 erately arched, and the individual teeth scarcely override one another. 

 But in Edestus, Campyloprion, and Helicoprion, not only is the coiling 

 caiTied to a remarkable degree, but the teeth are angulated so that their 

 bases either override or ensheathe one another. 



Respecting the disproportionate enlargement of the symphysial as 

 compared with adjacent antero-lateral series, this condition appears to 

 have been peculiar to Palaeozoic Cestracionts. We can almost certainly 

 pi'edicate its existence in Orodus, owing to the close similarity of its 

 teeth to those of Campodus. And although the lateral dentition of 

 Protodus, Edestus, Campyloprion, and Helicoprion has not yet been 

 identified as such, nevertheless it follows from our interpretation of this 

 class of remains that transverse rows of smaller teeth were present along 

 the sides of each ramus of the jaws. An understanding of Campodus 

 having once enlightened us as to the disparity between the symphysial 

 and lateral series of early Cestracionts, we are enabled to avoid the rather 

 formidable conception of giant sharks in the Carboniferous, armed each 

 with a mouthful of Edestus-like or completely coiled spirals, since there 

 is no evidence to show that Edestus, Campyloprion, or Helicoprion pos- 

 sessed more than one series, and this is to be relegated to the median 

 line in front. Absence of marks of wear in the symphysial teeth of the 

 three last-named genera, together with the difficulty of accommodating 

 a paired series larger than that of Campodus in the upper jaw, favor 

 the hypothesis that each individual possessed but a single arch, which 

 was located presumably in the lower jaw. Although corresponding in 

 position to the intermaudibular arch of Onychodus, and to the pre- 

 symphysial bone of Saurodon and Saurocephalus, it is obvious that no 

 homology exists, as has already been shown by Newberry and others 

 in commenting on Miss Hitchcock's interpretation.^ 



That the office of the symphysial dentition of Campodus was chiefly 



1 Ann. N. Y., Acad. Sci., Vol. IV. (1888), p. 118. Since the discovery of Heli- 

 coprion by Karpinsky and its reference by him to the snout region of an Elasmo- 

 branch, Jaekel has sought to revive Miss Hitchcock's original interpretation of 

 Edestus, regarding these structures " als Stossorgane, die aus dem Unterkiefer 

 vorgestreckt waren." Zeitschr. deutsch. geol. Ges., Vol. LI., 1899, p. 297. 



