Cope.J Ol-J [April.5, 



and narrowed at the extremities in a manner not seen in any of the known 

 vertebrae of G. natalis. 



Dimetkodon incisivus. Gen. et sp. nov. 



Char. Gen. Dentition as in Clepsydrops in the superior series. Pubic 

 bone not distinct from ischium. Humerus with trochlear condyles and a 

 denned proximal articular surface. 



The genus Dimetrodon embraces larger forms than the known species of 

 Clepsydrops. It is probable that the species had the neural spines in the 

 lumbar and dorsal regions elevated in the same way. The humerus while 

 of the same general character as that of Glepsydrops, differs remarkably in 

 its more perfect articular surfaces, indicating a terrestrial habit as distin- 

 guished from a probably aquatic one in the former genus. The supracon- 

 dylar foramen is present in this genus, and the proximal articular surface 

 winds obliquely round the expanded extremity of the bone. 



The separate jaws of D. incisivus show well the character of the den- 

 tal insertions. A strong thickening of the inner wall of the maxillary 

 bone is all that represents the palatine lamina. This enlargement 

 does not extend to the level of the external alveolar margin, which thus 

 forms a parapet. The roots of the teeth are long, and are contained in 

 deep alveoli of the palatine thickening ; but the portion of them which 

 projects beyond the alveoli is adherent to the external parapet by the side, 

 and hence the teeth appear to be pleurodont. They are shed in after the ab- 

 sorption of the root in consequence of the presence of the crown of the 

 successional tooth. The process commences at the inner alveolar border, 

 and extends inwards and upwards invading the palatine wall of the maxil- 

 lary bone. 



Dimetrodon is allied to Deuterosaurus Eichw. and Eurosaurus Fisch. as 

 defined by Meyer, the former known from a portion of the cranium, the 

 latter from bones of the skeleton. From the former it differs in the persist- 

 ence of the sutures separating the elements of the jaws, supposing the fig- 

 ure reproduced by Owen (Quar. Journ. Geol. Society, 1876, p. 358) to be 

 correct in the omission of them. Apart from this, Deuterosaurus has much 

 more elevated nostrils, more numerous incisor teeth, and wants the exten- 

 sive diastema in front of the superior canine. Lycosaurus Ow. from the 

 South African Trias resembles it much more nearly, bat does not present 

 the greatly enlarged anterior incisor teeth of Dimetrodon. 



Char. Specif. This saurian is established on the nearly complete pre- 

 maxillary and maxillary bones of the right side with the left maxillary of 

 the same individual. Associated with these are portions of the post- frontal, 

 frontal and nasal bones of the right side of perhaps the same individual, 

 but as the pieces are loose, this relation cannot be positively affirmed. Por- 

 tions of the maxillary, premaxillary and other bones, with isolated teeth 

 of numerous other individuals are in my possession. 



The first named specimens show that the mutual premaxillary and pre- 

 maxillo maxillary sutures are distinct. There is a deep emargination of 

 the border of the jaw at the latter suture, and the maxillary alveolar bor- 



