= 
Cope. | 512 [April 5, 
and narrowed at the extremities in a manner not seen in any of the known 
vertebrae of C. natalis. 
DIMETRODON 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 
defined 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 thesame way. The humerus, while 
of the same general character as that of Clepsydrops, 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. ¢tncisivuws 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 Hichw. and Hurosaurus 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. 858) to be 
correct in the omission of them. Apart from this, Deuterosawrus 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, but 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 isa deep emargination of 
the border of the jaw at the latter suture, and the maxillary alveolar bor- 
