NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 45 



readily distinguished from P 4 by the development and lingual posi- 

 tion of the tetartocone (hypocone). 



Deciduous lower premolars. — Dp 3 is much like P 3 but appears to 

 be a little more complex. The anterior crest seems more crescentic 

 and its anterolingual extremity is sometimes bifurcate or plicated 

 lingual to the paraconid. Also, in addition to the median posterior 

 crest which is much as in the permanent tooth, rather prominent 

 crests extend down the posterolingual and posterolateral slopes of the 

 protoconid nearly to the talonid. 



Dp 4 is almost indistinguishable from P 4 but is a trifle more elongate 

 in both the trigonid and talonid portions. Also, the anterointernal 

 extremity of the trigonid crescent is generally not recurved but there 

 is often a sharply angular flexure or style essentially comparable to 

 and paralleling the metastylid crest. In some Dp 4 's the anterior 

 extremity of this crest appears essentially bifurcate, almost as in 

 Dp 3 . The deciduous fourth premolar is also distinctly lower crowned 

 than the permanent premolar. 



VERTEBRAE 



Although ribs are rather poorly preserved in the available skeletal 

 portions of Meniscotherium and show very little of interest, which 

 also may be said of the sternal material, significant segments of the 

 vertebral column are included in at least three individuals, two repre- 

 senting M. chamense and one of M. robustum. 



Cervical vertebrae. — The atlas vertebra is decidedly short antero- 

 posteriorly, perhaps more so than in Phenacodus, and the transverse 

 processes are not widely expanded, although they appear to be a little 

 more extended than in the larger form. They rise anteriorly, and 

 just ahead of and above the anterior extremity on each side the large 

 foramen for the first spinal nerve is completely enclosed, opening 

 into the neural canal just posterior to the upper extremity of the 

 facet for articulation with the occipital condyle. A decidedly large 

 vertebrarterial canal opens forward on the inferior surface of the 

 transverse process and has its posterior aperture on the deeper pos- 

 terior margin of the transverse process, just lateral to the widest 

 part of the facet for the axis. These foramina appear to be very 

 much like those in the Phenacodus atlas illustrated by Cope (1884b, 

 pi. 57h) although relatively larger. 



The axis is much the longest vertebra in the neck and broadest 

 across the ventral surface of the centrum. The spinous process is 

 moderately high and relatively elongate anteroposteriorly but evi- 



