302 MEMOIRS OF THE CARNEGIE MUSEUM. 
epiphysis of the centrum is also missing. Specimen No. 1715 is a remarkably 
perfect little specimen, having sustained practically no injury whatever, all the 
processes and the articulating surfaces being well preserved. 
‘The dorsal spine in this vertebra is flattened. Viewed laterally, it projects 
strongly forward at its upper end, less prominently on its posterior margin. It is 
thickened transversely at its upper extremity and is rugose. The lamine pos- 
teriorly strongly overhang the centrum, and the postzygapophyses look outward, 
downward, and slightly backward. They are connected with the metapophysis 
by a narrow elevated ridge of bone between which and the anterior point of union 
of the lamine is a deep cavity lying between the spine and the metapophysis. 
The transverse process in specimen No. 1604 is formed by a process extending 
horizontally from the upper surface of the centrum and by a process arising from 
the side of the centrum less than one-third of the distance from its upper surface, 
which projects horizontally outward and backward. These two projections are 
united near their extremities by an outward narrow lamella or bridge of bone, 
which is directed obliquely backward and downward from the lower surface of 
the upper process and continued backward as an oblique process, pointing back- 
ward and outward. The arch formed by the union of these three encloses a large 
foramen which apparently accommodated a branch of the nerve passing out through 
the vertebral foramen (see Fig. 62). The same structure is found in the broken 
centrum of specimen No. 1708. No trace of such an arrangement is to be found 
in specimens Nos. 1703C, 1713, and 1715, the transverse process in all of these 
being a blunt narrow spine (see Fig. 63). The writer is inclined to regard this 
remarkable modification of the transverse process as indicating among other 
things a specific difference, and it is employed by him as one of the diacritic points 
of distinction between Moropus elatus Marsh and Moropus petersoni Holland. 
The prezygapophyses in all of the specimens look upward and somewhat strongly 
forward, but in specimens Nos. 1604 and 1708 they look far more strongly forward 
than in any of the other specimens. Their anterior extremities in Nos. 1604 and 
1708 are almost contiguous with the upper margin of the centrum, from which 
they are only separated by a very narrow groove, whereas in the other three speci- 
mens there is relatively a great distance between their upper extremities and the 
upper margin of the centrum, which they also overhang. In specimen No. 1604 
the prezygapophyses do not overhang the centrum, but their anterior extremities 
are located slightly behind the anterior margin; in specimen No. 1708 this feature 
is not so strongly marked. 
