OSTEOLOGY OF AMERICAN PERMIAN VERTEBRATES 379 



have been almost microscopical in size, and in none of the speci- 

 mens has the neck been preserved complete. 



A very perfect axis has been found among the loose material. 

 It is shown in Fig. 4, D. It doubtless belongs with one of the larger, 

 but not largest, skeletons; probably with the vertebrae shown in 

 Fig. 4, C. It measures just 8 mm. in length, and differs markedly 

 from any axis hitherto found in the American Permo-Carboniferous 

 deposits. It has a rather high, thin spine of more than half the 

 length of the centrum, its border sloping downward from above 

 the middle of the centrum to divide into the two postzygapophysial 

 processes. The anterior zygapophyses are unusually large, indicat- 

 ing a large atlantal arch. They are oval and are situated one on 

 each side of the base of the spine, their faces looking upward and 

 outward. The anterior end of the centrum is concave ; it is rather 

 narrow, and has an obtuse, keel-like process below; on each side 

 there is a winglike process continuous with the front surface for 

 the attachment of the cervical rib. The plane of the front end is 

 at a considerable angle with the long axis of the centrum. The 

 postzygapophyses are strong, but do not project far beyond the 

 centrum. The centrum has a strong keel below in front, becom- 

 ing linear posteriorly. The posterior surface of the centrum is 

 nearly circular in outline, and is at right angles with the long axis. 

 In the middle is a deep pit, which doubtless extends through the 

 centrum. 



Four posterior cervicals are associated in one specimen, belong- 

 ing with one of the smaller skeletons. They are shown in Fig. 

 4, A. The first two of these are of nearly equal length; they are 

 elongate and slender. On the side of the centrum in front there is 

 a winglike projection with a facet, as shown in Fig. 4, A, for the 

 articulation of a small, single-headed, cervical rib. Leading back- 

 ward and downward from this facet there is a distinct ridge, which 

 becomes obsolete before reaching the hind end of the centrum. 

 In the middle of the centrum, below there is a sharp, narrow keel. 

 The prezygapophyses are more prominent than the posterior ones ; 

 their articulai: surface looks almost directly dorsad. The third 

 vertebra of this series is not only shorter but it lacks the obHque 

 ridge from the costal facet. The fourth is still shorter, and has 



