Cope.] "-> [August 15, 



The premaxillary bones are distinct. The teeth of that bone and of the 

 maxillary are of unequal sizes. 



The axis has an expanded neural spine, and a diapophysis for rib articu- 

 lation, but no parapophysis or capitular fossa. The two latter features 

 characterize all the vertebrae which follow, as far as the lumbar series. 



The column in the typical specimen is tolerably complete, with a break 

 of uncertain, but probably not great length in front of the sacrum, and the 

 loss of the distal part of the caudal series. Intercentra of rather small 

 size are present throughout the series anterior to the sacrum. The inferior 

 faces of the caudal vertebrae are yet concealed by matrix. The bases of 

 the neural spines are compressed ; they were probably not elongate as in 

 Dimetrodon, though they are unfortunately broken off, except that of the 

 third cervicoclorsal vertebra. Here the spine is short and truncate above, 

 and rather wide anteroposteriorly. As in Dimetrodon there is no distinc- 

 tion between cervical and dorsal vertebrae. 



The pelvis is well preserved, and has the characters already assigned to 

 the O. natalis Cope.* The ilium has a process or narrowed continuation 

 with parallel sides, directed backwards and upwards, and bearing a keel 

 on the middle line on the internal side. The ischia are much produced 

 posteriorly, and are separated by a notch on the middle line posteriorly. 



The head of the femur is expanded, including probably the homologue 

 of the great trochanter of mammalia, and its articular face is crescentic, 

 with obtuse horns. There is a trochanter below it on the posterior edge 

 of the shaft. The condyles are inferior, and are separated by a deep 

 groove above and a shallow one below. The articular faces of the two 

 condyles are continuous, forming and go -shaped figure. The proximal ex- 

 tremity of the tibia is wider than the distal, and the articular face is unin- 

 terrupted. That of the distal extremity is a transverse oval. 



Specific characters. "While the vertebral centra of this species are rather 

 short, the bones of the head are very much attenuated, and the jaws are 

 long and slender. None of the four jaws is prefectly preserved, but the 

 number of the teeth in the maxillary bone may be approximately fixed at 

 thirty in a continuous series. One, and probably two of these, placed near 

 the anterior part of the series, are larger than the others. They are placed 

 at the position of the corresponding large maxillary teeth in Dimetrodon, 

 but they do not display the dimensions seen in the species of that genus. 

 To strengthen the jaw at this point, a rib rises from the thickened alveolar 

 portion, and extends vertically on the inner side of the thin facial plate of 

 the bone. The facial plate is double, and each lamina, except at the rib, 

 is not thicker than wrapping paper. 



The premaxillary bones are robust, and are excavated postero-laterally 

 for a very large nostril on each side. The spine is long. The alveolar 

 edge bears five teeth, which are followed by a diastema. These diminish 

 in size posteriorly, the'-first one being the largest, and equaling the large 



* Proceeds. Amer. Philos. Society, 1878, p. 509. 



