scott: toxodonta OF THE SANTA CRUZ beds. 
147 
processes of the seventh are short, heavy and imperforate, but have dis- 
tinct inferior lamellae. The neural arches are quite broad antero-pos- 
teriorly, so that the intervertebral spaces are very narrow. The neural 
spines vary much in height, but, unfortunately, it is not practicable to 
determine whether these differences are to be regarded as specific. In 
some individuals the spines are short and weak, in others very much 
stouter and better developed ; they increase in length posteriorly and that 
of the seventh cervical is, in some instances, almost as long and heavy as 
that of the first thoracic. 
In Toxodon the cervical vertebrae posterior to the axis do not differ in 
any significant manner from those of Nesodon. They are considerably 
shorter proportionately and have very heavy centra ; the transverse pro- 
cesses resemble those of the Santa Cruz genus, but on the third vertebra 
they are broader, more compressed antero-posteriorly, curving more back- 
ward and less downward, and on the sixth the inferior lamella has no such 
antero-posterior extension as in Nesodon. The neural arches are much nar- 
rower, having considerable intervertebral spaces, and the neural canal is 
relatively much larger. The neural spines are shorter and much more 
slender than in some specimens of Nesodon , but in others there is not so 
great a difference from Toxodon in this respect. 
While not definitely known, the number of thoracic vertebrae in Neso- 
don could not have varied much from 16-17, forming a very long thorax. 
The first thoracic in some respects resembles the seventh cervical ; the 
centrum is somewhat longer and has a less decidedly convex anterior 
face than in the latter and its shape is changed by the addition of the 
very large anterior rib-facets ; the transverse processes are very promi- 
nent and massive and bear very large and deeply concave facets for the 
tubercles of the first pair of ribs ; behind each process is a deep groove 
for the passage of the spinal nerve. The prezygapophyses are, as usual, 
of the cervical type and the postzygapophyses, which are on the hinder 
part of the neural arch, present laterally, not ventrally, and are some- 
what convex. The neural canal is of triangular shape and notably small 
and the spine, the exact length of which cannot be determined from the 
material before me, is relatively much stouter and presumably much 
longer than in Toxodon. 
The succeeding vertebrae of the anterior thoracic region (PI. XXI, fig. 
1 1 ) have short, heavy and slightly opisthocoelous centra, with large facets 
