150 MEMOIRS OF THE CARNEGIE MUSEUM 
specimen. The vertebra succeeding the thirteenth dorsal may or may not have 
supported arib. This vertebra has no distinct transverse processes, and there are 
no visible facets for the ribs on the sides of the centrum. In view of the fact that 
Cynomys has apparently no distinct transverse processes on the first lumbar, I shall, 
in this description, regard the vertebra under discussion as the first lumbar. 
The First Dorsal. — This vertebra has a less robust spine than is seen in Aplo- 
dontia, otherwise the neural arch is relatively as strong as in that genus. The short 
centrum has a plane surface inferiorly. The transverse processes are rather short 
and heavy, with a broad support for the tuberculum of the first ribs. The prezyg- 
apophyses are, as usual, placed low down on the arches, at the base of the transverse 
processes, while the postzygapophyses are higher up on the arch, in order to meet 
the articular surface of the succeeding vertebra. 
The Second Dorsal. —This vertebra is complete with the exception of the tip of 
the neural spine. ‘The latter is crushed to one side, which gives it a somewhat 
shorter appearance than the spine of the succeeding vertebra. The centrum is but 
slightly concave antero-posteriorly, and its diameter is very little greater than that 
of the first dorsal. The transverse process is strong, with a large tubercular facet 
for the second rib. The prezygapophysis is even lower down on the anterior border 
of the arch, than in the preceding vertebra, and does not extend so far beyond the 
arch anteriorly as in Aplodontia and Cynomys. The postzygapophysis is large and 
overhanging. 
The Third Dorsal.— With the exception of a longer and somewhat stronger 
neural spine, and the shorter transverse process this vertebra is very similar to the 
one in advance of it. 
The Fourth Dorsal.—'The fourth dorsal is complete, except the top of the 
neural spine. The centra in this portion of the dorsal region gradually increase in 
length proceeding backwards; they decrease in their transverse diameter, increase 
in the vertical dimension, and acquire a more concave surface inferiorly. The 
fourth dorsal has strong transverse processes, which point outward and upward from 
their base. The rib contact is strong. 
The Fifth, Sixth, Seventh, Highth and Ninth dorsals are so similar that the descrip- 
tion of one will answer for the entire series. 
The neural spines gradually become lower, the transverse processes shorter, and 
the antero-posterior diameters of the centra greater. The inferior surface of the 
centrum is more convex fore and aft in the eighth and ninth than in any of 
the preceding dorsals. In these vertebree, and the one in advance of them, 
the neural spines have lost their rounded form and gradually become laterally 
