66 REVISION OF THE PELYCOSAURIA. 



Original description : " Generic character. The neural arch is coossified, and the 

 zygapophyses and diapophyses are well developed ; the latter not elongate, and 

 standing on the base of the neural arch. The centra are notochordal. The inter- 

 centra are narrowed and transversely extended. The ribs are two-headed ; the capit- 

 ulum is received into a fossa of the posterior border of the intercentrum in advance 

 of the vertebra which supports the diapophysis, to which the tuberculum is attached. 



" C/mr. spec. — Centra with circular section at all points, and contracted at the 

 middle. No cariufe or grooves. The intercentra project beyond the edges of the 

 centra, gfiving the column the appearance of supporting annular ridges. Their lateral 

 angles extend upwards nearly to the base of the neural arch. The diapophyses are 

 short and are directed upwards and forwards ; their extremities are concave. The 

 zygapophyses are large and their articular faces nearly horizontal. The size of this 

 species is small, little exceeding that oi Bolosanriis striatiisy 



Measurements. 



m. nt. 



Lengthof centrum with intercentrum attached. .0.0056 Expanse of the diapophyses 0.0080 



Length of centrum 0040 heads of rib 0035 



^. , I Vertical 0035 Elevation to summit of neural canal oo45 



Diameters of centrum i ,, . ^ , 



(Horizontal 0035 



The original description is correct. 



About the size of LysoropJnis., the vertebrae are entirely different, lacking the 

 deep pit and carinse on the sides ; the articular faces are rounded out convexly, leaving 

 between them, when in position, a considerable space for the large intercentrum. 

 The neural arches are elongate antero-posteriorly and very low ; the spines are broken, 

 but were undoubtedly short. The articulation for the face of the rib on the inter- 

 centrum is peculiar. One side of the end is cut away leaving a step-like facet into 

 which the head of the rib fits. The ribs are double-headed with a strong tuberculum. 



The position of this form is very uncertain ; it may belong to the genns 

 Bolosaurns^ of which the vertebrae are unknown, or it \WA.y be entirely new. 

 The two vertebrae described is the only specimen in the two collections. 



Sphenacodon ferox Marsh. 



Am. Jnl. Sc, vol. xv, 1878, p. 410. 



Type: An imperfect lower jaw showing the anterior end. From El Cabre, 

 New Mexico. Preserved in the Museum of Yale University. 



Original description : " The crowns (of the teeth) are much compressed, and have 

 sharp cutting edges, without crenulations. In the present species the carnivorous 

 teeth are crowded together, and the crowns are placed slightly oblique, and twisted. 

 The jaws were comparatively short and massive. The rami of the lower jaws were 

 apparently united by cartilage only, and the symphysis was short. The vertebrae are 

 deeply biconcave." 



Measurements of the type of this species are as follows : 



mm. mm. 



Lengthof the dentary bone 150 Height above jaw of second lower tooth 15 



Space occupied by the teeth 130 Depth of dentary bone at symphysis 26 



Extent of four anterior caniniform teeth 25 Height of crown of compressed tooth 8 



Extent of twenty compressed teeth 105 Transverse diameter 4 



