26 REVISION OF THE PELYCOSAURIA. 



Measiiyements. ^ 



{Antero-posterior 0.018 

 Transverse oi? 

 Vertical 016 



( Antero-posterior 023 



Diameters of centrum No. 2 ■] Transverse 024 



( Vertical 026 



Expanse of anterior zygapophyses °^° 



Elevation of neural spine above zygapophyses 052 



. f Fore and aft 016 



Diameter of same at summit I .^^^^^^,^^^g ^^^ 



This vertebra is a posterior lumbar of Theroplcura retroversa. Thero- 

 pleiira triangnlata is therefore a synonym of Thcropleura retroversa. For 

 the revised description of the vertebrae, see p. 84. 



Theroplcura retroversa Cope. 



Clepsydrots h-ptocephalus Cope. Proc. Am. Phil. Soc, vol. xxii, 1884, p. 30. Also Pal. Bull. 39. 

 Diofeus leftocephalus Cope. Trans. Am. Phil. Soc, vol. xvii, 1892, p. 11. 



Type : The imperfect skull ; the uearly complete vertebral columu ; the complete 

 pelvis ; both femora and tibia. No. 4155 Am. Mus. Nat. Hist., Cope, coll.; froui Big 

 Wichita river, Texas. 



Original description 0/ the synonym : " While the vertebral centra of this species 

 are rather short, the bones of the head are ver>' much attenuated, and the jaws are 

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

 the teeth in the maxillar>' bone may be approximately fixed at thirt)' 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 poiut, a rib rises from the thick- 

 ened 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 iu size posteriorly, the first 

 one being the largest, aud equaling the large maxillary teeth. The last two are quite 

 small, less than the usual maxillary teeth. 



"The dentary bones are very slender, aud the distal end is somewhat thickened 

 to support two teeth larger than the others. These are the third and fourth from the 

 extremity, and are not quite so large as the large teeth of the maxillary bone. The 

 remaining mandibular teeth are small, and are not so much compressed as in the spe- 

 cies of Dimetrodon. Many of them have only a posterior cutting edge, which is not 

 denticulate. The apices are strongly turned backward in the posterior part of the 

 series. The posterior part of the dentary bone rises and carries some of the teeth with it. 



" The surface of the free edge of the internal plate of the pter>goid bone is 

 granular. The teeth on the posterior edge of the same are subconic, and in a 

 single series. 



