NO. 2 



A STUDY OF MENISCOTHERIUM — GAZIN 



47 



noted by Cope, the centra are slightly opisthocoelus and the articular 

 surfaces distinctly oblique. 



Dorsal vertebrae. — The number of dorsal vertebrae in Menisco- 

 therium is not known, although it was probably close to that of 

 Phenacodus which was given by Cope as 14 or 15. In one of the 

 articulated series at hand (see fig. 5 ) only the first seven are preserved 

 in place and in another the last six. These show a decrease in size 

 from the cervicals, but there is a surprising increase in size near the 

 posterior limit of the sequence and into the lumbars. The anterior 

 dorsals are only slightly shorter than the cervicals but noticeably 

 narrower across the zygapophyses and the centra are dorsoventrally 

 flattened. The neural spines, after the first, are rather slender and 



Fig. 6. — Meniscotherium robustum Thorpe. Cervical and anterior dorsal ver- 

 tebrae (U.S.N.M. 18283); a, dorsal view; b, ventral view. ^4X natural size. 

 Knight member, Wasatch formation, Green River Basin, Wyo. 



backward directed in the anterior part of the series, but posteriorly 

 they become shorter, more erect, and anteroposteriorly wider, with 

 the last one or two tilting forward. The transverse processes carrying 

 the articular surface for the tubercle of the rib are markedly elongate, 

 at least in the first seven, and rudimentary metapophyses extending 

 upward from the transverse processes above the tubercle facet, 

 although mostly damaged, are evident. Posteriorly the facet for the 

 tubercle of the rib is supported by more of a pedicle extending antero- 

 ventrally from the transverse process, and the metapophysis becomes 

 better defined and separate from both. In the fourth from the last 

 dorsal the three structures are joined in a common base, and the 



