ICHTHYODORULITES. 141 



ICHTHYODORUUTES. 



This group is purely artificial, and is used merely as a reposi* 

 tory for various spines, dermal armature, tubercles, etc., of such 

 cartilaginous fishes as sharks and chimseras, which are only 

 known from fragmentary remains. It often follows that 

 such incomplete indications of these animals are very similar in 

 the various genera, and that their determination as to higher 

 rank is very difficult, if not impossible, for which reason it would 

 be convenient to at least indicate them in this provisional ar- 

 rangement. About 82 genera have been described. 



Genus CYLINDRACANTHUS Leidy. 



Cylindracanthus Leidy, Proc. Acad. Nat. Sci. Phila., VIII, 1856, p. 12. Type 



Cylindracanthus ornatus Leidy, monotypic. 

 Ccelorhynchus (nee Giorna) Agassiz, Poiss. Foss., V, 1843, pp. 892. Type 



Ccclorhynchus rectus Agassiz, first species, and name only, restricted by 



Hay, Bull. U. S. Geol. Surv., No. 179, 1902, p. 331. 

 Glyptorhynchus Leriche, Poiss. Eoc. Basin Beige, 1906, p. — (not consulted). 



Spine very long, slender, gradually tapering, rounded in sec- 

 tion, without denticles, external face longitudinally ridged and 

 grooved, each ridge corresponding to wedge-shaped plate which 

 forms small sector of spine. Central cavity relatively small, 

 sometimes in part simple, but usually divided by median parti- 

 tion. Division plane passing through middle of partition, thus 

 allowing spine to be readily split into two symmetrical halves, 



This genus was originally thought to be possibly allied with the 

 sword fishes, and others have thought it located near the chimse- 

 roids. Its true position must still be considered doubtful. 



Cylindracanthus ornatus Leidy. 



Cylindracanthus ornatus Leidy, Proc. Acad. Nat. Sci. Phila., 1856, p. 12. 



Cretaceous near Pemberton, Burlington Co., N. J. (W. Taylor), and 



Alabama. 

 Ccelorhynchus ornatus Cope, Proc. Amer. Philos. Soc. Phila., XI, 1870, p. 



294. (Eocene Marl of Farmingdale, Monmouth Co., N. J.) 



Spine cylindrical, slightly tapering (both ends damaged). 

 Surface with longitudinal strise of more or less even length, 



