10 MEMOIRS OF THE CARNEGIE MUSEUM 
form a widely open V. The supra- and infrapostzygapophysial cavities are very 
deep and at the bottom the latter is subdivided into three unequal pockets by two 
short, delicate laminze. On the posterior surface of the neural spine there is a 
median rugose surface suggestive perhaps of a postspinal lamina. 
As has already been remarked, the series of vertebree was interrupted at the 
first dorsal and a number of the succeeding vertebree are missing from the series. 
I have estimated the number of missing dorsals at four, the second, third, fourth 
and fifth. 
it is, as will appear later, the first dorsal of the series of nine mentioned above as 
If this estimate is correct, and there are many reasons for believing that 
pertaining to this skeleton would be the sixth of 
the dorsal series. That these two series of verte- 
bree. pertained to one and the same skeleton is 
demonstrated beyond the possibility of a reason- 
able doubt, not alone by their proximity to one 
SN 
EX 
e ) 
another in the quarry where they lay imbedded in 
the sandstone as shown in Figs. 1 and 2 at B. 572 
and C. 572, but by the relative sizes of the verte- 
bree, their color and texture and the entirely closed 
sutures of the neural arches, indicating in each in- 
stance an animal of identically the same age. 
Figs. 3 and 4 are side views respectively of the 
supposed sixth and the first dorsal. They are intro- 
duced here for direct comparison with one another 
> 
Fie. 3. Sixth (?) dorsal of type of 
572) 
seen from right side, 5 natural size, 
pA, lamina; 4, become more apparent after an examination of 
horizontal lamina ; ol, oblique lamina. 
Ronloceniiiocommnn prtccns ONO. and to show the great disparity in structure exist- 
ing between these two vertebrae. These differences 
postzygapophysial 
Se ee ee ae plate A, where posterior and anterior views of the 
IG. 4. ivs orsal Of Same, same 
view ; ol, oblique lamina ; al, inferior 
blade of diapophysial lamina ; ¢, tuber- 
cular rib facet ; ¢, capitular rib facet ; 
S, surface for muscular attachment of 
scapula, 7; natural size. 
the transverse processes and the height and form of the neural spine. 
same vertebree are also given. 
The greatest structural differences exhibited in 
these two vertebree are to be found in the relative 
height of the neural arches, the form and position 
of the capitular rib facets, the form and positions of 
All these and 
many other differences of only less importance will become apparent as we describe 
the sixth dorsal in detail. 
Sixth ? Dorsal (Plate I., Fig. 6).— This vertebra is complete save a small 
part of the anterior end of the centrum and a portion of the upper part of the 
