52 M. G. MEHL 
The lower side of the centrum is markedly concave anteroposteriorly 
and distinctly convex from side to side at mid-length. 
The diapophysis is somewhat longer than the parapophysis. 
Both arise from about the mid-length of the vertebrae, the former 
from the arch and the latter from the centrum. They are united 
for a short distance at their base. Both increase in diameter 
toward the distal end where they are distinctly enlarged. 
In the described forms of Diplocaulus the neural spine has 
but little development. It is usually little more than a sharp, 
ridgelike thickening of the arch over the neural canal. In the 
vertebrae herein described one of the most conspicuous features 
is the spine development. For the most part the spines are com- 
paratively high with flat, more or less rugose tops. The first of 
the series is distinctly expanded laterally at its top. It is only 
in the last two of the series that there is a suggestion of the sharp, 
keel-like degeneracy of the spine and even in these two vertebrae 
it rises distinctly above the arch. The ratio between the portion 
below and above the plane of the zygopophyses throughout most 
of the column is 4:7 while in the average previously known form 
the ratio is 4:4. In the last two vertebrae of the present speci- 
men the ratio is about 4:5. ; 
One of the characteristic features of the vertebrae of Diplocaulus 
is the presence of a pitlike depression on the top of the spine. 
There is a great variety in this pit development ranging from very 
small, round openings to rather pronounced, laterally elongate 
depressions. In one string of eleven connected vertebrae, No. 1016 
in the Walker Museum Collections, the pits seem to be entirely 
lacking in all back of the fifth. The first pit is in the second 
vertebra in every case. Usually it is very conspicuous and more 
or less quadrangular in shape. The third vertebra apparently 
lacks the pit. In the following vertebrae the number with pits 
probably varies from individual to individual. For the most part 
there is no suggestion of an anteroposterior constriction or division 
of the pit into two distinct facets and in no specimen except the 
one herein described has the writer seen distinctly double pitting. 
In the present specimen, however, in each vertebra except the first 
of the preserved series which is pitless, the spine depressions are 
