SYSTEMATIC REVISION OF THE SUBORDER. 55 



bones of the limbs. Many of these pieces are preserved in continuous masses, thus 

 greatly aiding 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 Clepsydrops ; 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 dentar}' bone can not be precisely stated, but it 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 dentig- 

 erous bone is quite diflferent 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 pro- 

 cess are dentigerous ; the one bears a single series of four large teeth ; and the adja- 

 cent angle and side bear numerous small teeth. 



" The vertebrse have the elongated neural spines of the allied genera, and they are 

 simple. The centra have curved articular margins indicating the presence of inter- 

 centra, 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 vertebrse, apparently from the posterior part of the col- 

 umn, 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 

 lateral ridges of the T. iriangulata are situated low down on the centra. The diapo- 

 physes supporting the tubercular articulation are frequently elongate. 



"The scapular and pelvic bones are of the usual type. The humeri belong to fonn 

 second of my Pal. Bull. No. 29. They have rather slender shafts, and much expanded 

 extremities. The proximal articular surface is well defined. The supracondylar 

 foramen and other points are as in the Pelycosajiria generally. There were probably 

 distal condyles, but this is not absolutely certain." 



Measurements. 



»!. m. 



Length of mandibular series of teeth (nearly Length of another centrum on the same block ..0.020 



complete) on block o. no Diameters of humerus (separate); 



crown of mandibular tooth 008 Of head ; 



Antero-posterior diameter of mandibular tooth.. .004 Larger 065 



Diameters of the articular extremities of a ver- Smaller 013 



tebra on the same block; Of shaft 017 



Vertical 021 



Transverse 020 



For description of the homeotype see the morpliological description. 



The spines and the character of the skull show that this animal was 

 far more advanced in development than the Poliosauridce and was a true 

 member of the Clepsydropidce. 



