VERTEBRATES. 91 



The various forms of teeth constituting the dentition of Dcltopty - 

 chius have been in all cases recognized from isolated detached 

 specimens, save in the instance of the maxillary posterior and median 

 serial teeth. In the latter we have authentic evidence of specific 

 identity, in the discovery by Mr. Wachsmuth of a specimen show- 

 ing the teeth in actual material juxta-position. Wherever the one 

 form occurs there also is found the others, and taking this fact into 

 consideration and what is known of the various forms of teeth be- 

 longing to the genera Cochliodus, Ortkopleurodus, etc., the association 

 here conjectured seems to be amply warranted. The genus as here 

 defined bears intimate relationship with Cochliodus and Chitonodus, 

 holding an intermediate position between the latter and Vaticinodus 

 and Stenopterodus. It is, however, distinguished from the former by 

 peculiarities in the coronal contour of the maxillary posterior teeth, 

 and the greater obliquity cuneate outline of the mandibular posterior 

 form, but chiefly in the character of the enameled abrupt antero- 

 lateral border of the latter form, which in Cochliodus presents a 

 narrow fold precisely like that along the postero-lateral border, also 

 as occurs in either lateral border of the maxillary posterior form. 

 This, in view of the uniformity of the articular borders in the vari- 

 forms of Cochliodus, Chitonodus and their intimate allies, might be 

 regarded as inconsistent with the conjectured association of forms 

 in the present generic group of teeth. But after all it seems in 

 some sort to foreshadow or form a transition from the true Cochlio- 

 dus type to that of Pcecilodus, the mandibular posterior form of 

 which possesses much the same character of steep enameled antero- 

 lateral border as obtains in the homologous form of the present 

 genus ; in both of the latter genera the articular border of the 

 opposed maxillary form partakes still to a most intimate degree of 

 the character of typical Cochliodus. 



The genus is apparently confined to the measures of the Lower 

 Carboniferous period, representative species occurring in each of the 

 successive formations beginning with the Upper Burlington, and 

 includes the form described by Dr. Leidy under the name Coch- 

 liodus nitidus, of the Chester formation. 1 



According to the above interpretation of the facts, the genus pos- 

 sesses precisely similar diagnostic terms distinguishing the form 

 referred by authors to the "anterior" tooth of Deltoptychius acutus, 



. Am. Phil. Soc,, vol. xi, p. 87, PL v, f. 2. 



