MORPHOLOGICAL REVISION OF THE SUBORDER. 



129 



Texas. No. 4035 Am. Mus. Nat. Hist., Cope, coll. : Nine anterior vertebrae in con- 

 nection, beo-inning with the axis, and after a break six posterior dorsals in connection. 

 Spine nearly complete. No. 28 University of Chicago : A fragment of lower jaw. 

 From Coffee Creek, Vernon county, Texas. No. 4064 Am. Mus. Nat. Hist., Cope, 

 coll. : A fragment of the lower jaw shows that the bases of the teeth were decidedly 

 oval in section. This is different from other species where the teeth are rounded or 

 quadrate at base; it occurs in a second specimen. No. 28 University of Chicago. The 

 base of the large maxillary canine is quadrate in section, but nearer the middle it is 

 nearly hemispherical in section, the outer side being much more convex than the 

 inner. There are two teeth in the maxillary portion of the diastemal notch. 



The character used by Cope to distinguish this species, the prominent intercen- 

 trum, is common to all species of the genus, but the forward inclination of the axis 

 and neural arch is a feature unique in the species. The more 

 posterior vertebrae of the type specimen are closely similar to 

 DimetrodoH incisiviis. A posterior dorsal shows the low keel to 

 be divided by a shallow longitudinal groove. The spines of the 

 vertebrae are smooth. The astragalus is rough 

 and rugose, much stronger than any other 

 astragalus in the collections (plate 16, fig. 8). 

 No. 114 University of Chicago: The 

 skull is ver>' similar in outline to that of 

 Dimelrodon incisivtis. The section of the 

 teeth can not be made out, but there are three 

 teeth in the maxillary portion of the diaste- 

 mal notch. This seems to be a distinctive 

 character of the species ; in several specimens 

 of the genus there is a single tooth preceding 

 the enlarged maxillary, but in others there is 

 none or a scar showing where a single tooth 

 has been lost, but never more than one. The 

 diastemal notch is nearly filled with teeth; 

 this is a primitive character and would indi- 

 cate that the species was perhaps the least specialized of the genus. In this skull both 

 large maxillary teeth are functional at the same time. 



The vertebral column : The a/las is similar to Dimetrodon incisivus. 

 The axis has the centrum similar to Dimetrodon incisivus^ but the posterior end 

 of the centrum is much lower than the anterior, so the whole vertebra slants down- 

 wards to the rear, and if the bottom line of the centrum is horizontal the spine slants 

 forward. The spine is proportionately much wider antero-posteriorly and extends 

 farther out over the atlas ; the upper end has a triangular facet for the ligament ; the 

 posterior edge, while wide, is not excavated by a deep groove as in Dimetrodon incisi- 

 vus ; the anterior edge has two small surfaces for ligamentous attachment. 



The tliird cervical has the spine short and very slender ; it curves sharply forward 

 and lies close to the posterior edge of the neural spine of the axis. The whole neural 

 arch stands far forward over the anterior part of the centrum, giving the vertebra the 

 characteristic inclined appearance as opposed to the vertical condition of the same 

 vertebra of Dimetrodon incisivus. 



54 



55 



Fig. 54. — Lateral view of an anterior cervical of D. dol- 

 lovianus. No. 4064 Am. Mus. X yi. 



Fig. 55. — Anterior view of the same vertebra as fig. 54. 

 X I. Sfiowing tfie large intercentrum and 

 facets for the ribs, on which evidence Cope 

 referred this species to the genus Embolophorus. 

 //f, intercentrum. 



