Measurements. M. 



Length of alveolar edge of mandible 120 



' ' from diastema to canine tooth 030 



" of centrum of atlas 010 



"axis 018 



" " centra of following five vertebra; 07L 



" " ilium at acetabulum 040 



The lanciform shape of the skull with its consequent peculiarities distin- 

 guishes this species from the Clepsydrops natalis, and the Dimetrodon in- 

 ciswus. The canine tooth is more posterior, the teeth more numerous, 

 and the alveolar borders less curved than in either of those species. The 

 diastema is less excavated, and the muzzle less obtuse. 



Theropletjra obtusidens, sp. nov. 



This species is represented by nearly all parts of the skeleton, including 

 jaws of both sides with teeth, numerous vertebrae, and bones of the limbs. 

 Many of these pieces are preserved in continuous masses, thus greatly aid- 

 ing in the identification of parts. 



Although the species is not larger than the Theropleura retroversa, the 

 neural arches are coossified with the centrum. 



The jaws are long and rather slender, and there is no such inequality in 

 the sizes of the maxillary teeth as in the genera Dimetrodon and Clepsy- 

 drops ; the canine being scarcely larger than the others. The crowns are 

 elliptical in section at the base, with straight sides ; the sections of the 

 crowns are lenticular, and the apices are not very acute. The superficial 

 coating is striate with fifteen or sixteen rather obtuse ridges The cutting 

 edges are not very acute, nor are they denticulate. The number of teeth 

 in the dentary bone cannot be precisely stated, but is about twenty-one. 



The mandibular articular face consists of two open parallel grooves, one 

 shorter than the other, extending obliquely to the long axis of the jaw. 

 The palatal dentigerous bone is quite different from that of Dimetrodon. Its 

 inferior face instead of being narrow, is rhombic. The ascending process 

 arises from one of the terminal angles of the rhomb, and the horizontal 

 process continues from the opposite angle in line with the inferior surface. 

 The borders of the rhomb next to the ascending process are dentigerous ; 

 the one bears a single series of four large teeth ; and the adjacent angle and 

 side bear numerous small teeth. 



The vertebrae have the elongated neural spines of the allied genera, and 

 they are simple. The centra have curved articular margins indicating the 

 presence of intercentra, which are, however, not preserved. Traces of 

 sutural articulation with the neural arch remain. Many of the centra are 

 much compressed and have a narrow sharp median keel. In a few vertebra?, 

 apparently from the posterior part of the column, an angular ridge extends 

 posteriorly from the base of the diapophysis ; this is apparent also on a 

 caudal centrum. This point is characteristic of the T. retroversa, but I do 

 not find the large capitular facet of that species in the T. obtusidens. The 



