26 THE SAUROPOD DINOSAUR BAROSAURUS MARSH. 
however, is nearly perfect, except for the rarely preserved diapophyses, of which only a 
portion of the left is present. This Barosaurns caudal differs from that of Diplodocus, 
moreover, in that the diapophyses arise lower down on the vertebra, being almost entirely 
below a line drawn from the upper limitations of the faces of the centra, whereas in 
both D. carnegiei and D. longus of the American Museum the diapophysis arises above 
a line thus drawn. In D. longus the entire diapophyses are visible when viewed on a 
level from in front, in Barosaurns they are hidden by the expanded faces of the 
centrum. The centrum is deeply constricted in the middle, with a concave anterior face 
and a flattened posterior one. Laterally it bears deep pleurocceles which are relatively 
long and low. In the present instance, the median partition between the pleurocceles is 
broken through, but in the succeeding caudal it is about 20 mm. thick, which must have 
been approximately true of the present bone. There is on the under face of the centrum 
the longitudinal hollowing so characteristic of Diplodocus. In fact, in Marsh's descrip- 
tion of that genus (1878, p. 414) he says: "It may be distinguished from the genera 
already known by the caudal vertebra;, which are elongated, deeply excavated below, 
and have double chevrons, with both anterior and posterior rami" — a definition which 
would apply equally well to Barosaurns. The median hollow is accentuated as one 
goes further back in the caudal series. The neural arch is strong ; the spine, slanting 
backward at an angle of 45 degrees, is expanded and rugose at the summit. The width 
of the summit is 96 mm., and the antero-posterior diameter 126 mm. Beneath the 
expanded portion the transverse diameter is 42.5 mm. Prominent but thin buttresses, 
the prezygapophysial lamina;, run up the front of the spine, the prespinal lamina being 
confined between them except toward the summit, where it expands to meet the terminal 
rugosity. The prezygapophyses are well developed, jutting about 65 mm. in front of 
the centrum. The articular face looks upward and inward at an angle of 45 degrees 
and is comparatively flat. The postzygapophyses underlie the spinous process and do 
not extend beyond the limits of the centrum. Their articular faces are somewhat curved 
and look downward and outward. Both pre- and postzygapophyses are well buttressed 
from the pedicels by the zygapophysial laminae. 
The centrum is proccelous, the curvature of the anterior face being such that the 
ratio of the depth of the concavity to its width is as 1 : 8. There are well marked 
chevron facets at the posterior end of the centrum, which seem to imply a backwardly 
directed chevron similar in angulation to the spine. 
In Diplodocus longus the spine is much more erect than in Barosaurns nor is the 
summit expanded as in the latter genus. 
Measurements of Caudal XIII Barosaurns 
lentus 
mm. 
Height over all 445 
Centrum, length 245 
anterior face, height 215 
" width 252 
posterior face, height 216 
" width 220 
Pleurocoele, length 100 
height 35 
Neural spine, width of summit 96 
