PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 59 



has been left in matrical association with the cervical vertebrae. The ventral ribs are 

 figured as nearly as possible as they were found on the left side, the under side as the 

 skeleton lay in its matrix, filling up most of the open space below the ribs in front 

 of the pelvis and extending forward quite to the hind end of the interclavicle. It is 

 evident that there was no cartilaginous sternum in life back of the coracoids. 



HABITS AND RELATIONSHIPS. 



The relatively large size of the skull of Ophiacodon is very conspicuous in the 

 restoration. It is quite a third of the length of the body to the base of the tail, 

 and doubtless more than a sixth of the entire length of the creature. It was very 

 narrow and high, and had an inconsiderable weight in life, notwithstanding its 

 length, composed as it is of very thin and delicate bones. The nostrils and eyes 

 were relatively small, though quite large enough for the body. The legs are short 

 and stout, with broad feet and flattened ungual phalanges; and the tail was slender 

 throughout. Without taking into account the character of the claws, it is evident 

 that Ophiacodon was neither a swimming nor a burrowing animal; its tail would 

 have been of no use in the water in propulsion ; and the front legs were not nearly 

 long enough to excavate a hole for the head to enter. And it is also apparent 

 that Ophiacodon was not a swift-moving reptile. Doubtless, like so many of its 

 congeners, it spent its life about the fiat marshes and low plains, feeding upon 

 such small reptiles and amphibians as it could capture which did not require 

 much speed, since nearly all were sluggish creatures possibly varying its diet 

 with soft-bodied invertebrates. Its long, slender and recurved teeth were well 

 adapted for the capture of slippery creatures, but, with the jaws, they were too weak 

 to withstand much struggling of strong-bodied prey. 



Aside from Theropleura, the relationships of Ophiacodon are not very intimate 

 with any known reptiles. That it should be located in the same suborder with the 

 true Pelycosauria seems altogether reasonable, notwithstanding the paired tem- 

 poral vacuities and the holocephalous ribs. The pelvis, especially, has the very 

 characteristic elongation of the pubes, projecting far in advance of the true pelvic 

 brim ; and the puboischiadic vacuity is as in Dimclrodon and Varanosaurus. The two 

 sacral vertebra;, a not very profound taxonomic character, allies the form with 

 the Poliosauridae. The relatively short spines, of vmiform length, are like those of 

 Varanosaurus and its allies, though, unlike them, the anterior ones are thickened, 

 doubtless for the better support of the elongated head. That the extraordinarily 

 elongate spines of Dimetrodon is a very important taxonomic character does not 

 seem as probable as formerly, since there is now but little doubt that the spines 

 of Sphenacodon are not unlike those of Ophiacodon, though the skull and dentition 

 seem to be quite like those of Dimetrodon. 



It is very probable, if not certain, that the genus Theropleura, from the Texas 

 beds, is a closely allied, if not identical genus. The vertebras, Hmb bones, and such 

 parts of the skull as are known, as figured by Case (Cam. Inst. Wash. Pub. No. 55, 

 pis. 3 and 13) all resemble the corresponding parts of Ophiacodon closely. Mandi- 

 bles and maxillae from the Craddock bone-bed in Texas, mentioned by Williston 

 as probably belonging in a new genus,* are also very like the same parts in Ophia- 

 codon, save that the teeth are more compressed. 



If Ophiacodon and Theropleura are eventually found to be closely allied but 

 distinct genera, it may become advisable to separate them into a distinct family, 

 the Ophiacodontidae. For the present they may both find a place in the family 

 Poliosauridae. 



* American Permian Vertebrates, p. 75. 



