150 Dr. C. R. Eastman — New Form of Shark'n Dentition. 



undoubtedly that there were Palgeozoic sharks with sharp, piercing^ 

 teeth, which were never shed, but became fused into whorls as the 

 animal grew." 



The same memoir was also reviewed by the present writer,^ who 

 brought forward additional instances of coiling amongst Palaeozoic 

 sharks, and was inclined to look upon the segments of Helicoprion 

 as veritable teeth. Finally, a fortunate discovery of the symphysial 

 dentition of the Carboniferous genus Campodus, made by Professor 

 E. H. Barbour, Director of the Nebraska University Geological 

 Survey, threw new light on the matter, and furnished ground 

 for a positive statement that the fused segments of Edestus and 

 Helicoprion are actually teeth belonging to the anterior series of 

 Cestraciont sharks. The evidence for this was presented by the 

 writer before the Denver meeting of the American Association for 

 the Advancement of Science, and in the published abstract of that 

 paper ^ the arrangement of the anterior series in Campodus variabilis 

 (Newb. & W.) was briefly described. A second specimen in the 

 Museum of Comparative Zoology at Cambridge, Mass., from the 

 Coal-measures of Osage County, Kansas, exhibits the symphysial 

 series in natural association with the lateral. Professor Barbour's 

 specimen, shown in the accompanying Plate YIII, Fig. 1, is more 

 perfect in some respects, but has none of the lateral series associated 

 with it. 



Each individual of Campodus is known to have possessed at least 

 three series of coalesced anterior or symphysial teeth. As indicated 

 by the marks of contact, there was a median arched azygous series 

 in one jaw (presumably the lower, as is the case in Cestracion, 

 Ghlamydoselache, and other existing sharks), opposed to which in 

 (presumably) the upper jaw were two corresponding series separated 

 from each other by a slight interval. The orientation of both the 

 symphysial and lateral teeth of Campodus may be determined from 

 the fact that their coronal buttresses are directed outward, instead 

 of inward, as was erroneously supposed by Messrs. St. John and 

 Worthen. Several series of anterior teeth, all coiled in a single 

 plane, are known to have been present in the same mouth of 

 Campodus, Protodus, Periplectrodus, and certain Cochliodonts, hence 

 it is probable that a like condition was true of Edestus and 

 Helicoprion. In the two last-named genera it was rightly pointed 

 out by Smith Woodward that the absence of lateral facettes or marks 

 of contact with adjoining whorls indicates that the series were 

 separated from one another, as in the existing Ghlamydoselache. 

 In the light of the now clearly apparent odontological nature of 

 Edestus and Helicoprion, together with their Cestraciont affinities, 

 it may be pertinent to inquire whether the huge fin-spines from the 

 Carboniferous, such as Oracanthus, Phoderacanthus, Stichacanthus , 

 and the like, were not borne by creatures having an Edestus- or 

 Campodus-like dentition. 



1 Amer. Nat., 1900, vol. xxxiv, ]). 579. 

 ^ Science, n.s., 1901, vol. xiv, p. 795. 



