PETERSON : DESCRIPTION OF NEW RODENTS 149 
in front. Posteriorly, the neural arch overhangs the superior part of the short 
spinous process of the third cervical, so that the anterior part of the arch of the latter 
is entirely within the arch of the axis. In the cotype (No. 1208), the third cervical is 
entirely codssified with the axis (Pl. XVIII, Figs. 9,9a and 9b.) The articulation for 
the atlas is extended well up upon the anterior border of the neural canal. The odon- 
toid process is a heavy rounded peg. The delicate transverse processes are broken 
off on the axis and the third cervical. 
The Third Cervical. — The third cervical is charactistic in 8. fossor, on account of 
its tendency to become coéssified with the axis. In the type, this vertebra is clearly 
separated from the axis, but the encroachment of the latter bone on the third cervical 
shows that in old individuals these two vertebrae may become codssified. In the 
type the neural spine is not so high as in Aplodontia, and the centrum has the same 
antero-posterior diameter as in that genus. 
The Fourth Cervical. —'This vertebra is represented by the centrum and half of 
the neural arch in the type specimen. The centrum is short antero-posteriorly, even 
shorter than the centrum of the third. Transversely, the centra are broad, and de- 
pressed vertically. The fourth cervical appears to have a heavier transverse process 
than in Aplodontia. 
The Fifth Cervical. —'The fifth cervical is almost identical in form with the fourth. 
The neural arch and spine are somewhat heavier than in Aplodontia, and the trans- 
verse processes appear stronger. The neural canal is large. The vertebrarterial 
canal-is smaller thanin Aplodontia and Cynomys. ‘The prezygapophyses are directed 
forward and downward, and postzygapophyses upward and backward. 
The Siath Cervical. —The neural arch is injured, and the transverse processes of 
this vertebra are lost. The antero-posterior diameter of the centrum is less than in 
the preceding vertebra; otherwise there is not any marked difference between these 
two bones. 
The Seventh Cervical.—The neural arch is low and broad, similar to that in 
Aplodontia, but heavier. The spine appears shorter. ‘The antero-posterior diameter 
of the centrum is but very little greater than that of the preceding vertebra. The 
transverse processes are heavy, and are directed horizontally outward from the cen- 
trum, not postero-laterally as is the case in all the preceding vertebree. There is a 
distinet facet for the first rib on the posterior face of the centrum. ‘This vertebra 
has no vertebrarterial canal. 
As a whole, the cervical region is comparatively short and broad. With excep- 
tion of the shape of the third cervical, the neck is similar to that of Aplodontia. 
Dorsal Vertebre. — There are thirteen dorsals more or less complete in the type 
