scott: toxodonta OF THE SANTA CRUZ beds. 
207 
the latter genus and has a similar dependent hook given off from the 
inner end. The anterior border of the ascending ramus is narrower than 
in Nesodon and the lineae obliquae are very obscurely marked, except dis- 
tally, where the internal border becomes very prominent, but the fossa 
behind the last tooth is much shallower than in the other genus. 
No part of the hyoid apparatus is preserved in connection with any of 
the skulls and I am therefore unable to say whether the place of attach- 
ment is the same highly exceptional one as in Nesodon , or not, though 
one decided difference from that genus should be noted. In Nesodon 
almost every well preserved adult skull shows the stylohyal ankylosed 
with the anterior end of the bulla, but I have seen no instance of such 
ankylosis in Adinotherium. 
Vertebral Column and Ribs. — So far as can be determined from the 
available material, the vertebral formula appears to be the same as in 
Nesodon , viz.: C. 7; Th. 16-17; L. 4-5; S. 6; Cd. ? The neck is short 
and rather weak and the individual vertebrae closely resemble those of 
Nesodon , with such differences of detail as would naturally occur in a 
much smaller and lighter animal. 
The atlas (PI. XXVI, figs. 7-9) is very short antero-posteriorly and very 
broad transversely ; the anterior and posterior cotyles are quite as 
in Nesodon , on a smaller scale, but the neural arch is narrower and 
more slender and has a more pronounced upward curvature, and the spine 
is quite obsolete, or very faintly indicated. The inferior branch of 
the first spinal nerve perforates the base of the transverse process, but the 
ventral opening of this canal is more widely separated from the anterior 
opening of the vertebrarterial canal than in Nesodon. — Except for its 
smaller size and lighter construction, the axis (PI. XXVI, figs. 10, n) is 
very like that of the latter genus ; it has a short centrum which is 
very broad anteriorly, contracting abruptly behind the transverse pro- 
cesses. The following small differences from the axis of the larger animal 
may be observed : (1) The odontoid process is more cylindrical and more 
abruptly truncated at the free end. (2) The anterior cotyles are propor- 
tionately narrower transversely, higher and more convex dorso-ventrally 
and they are separated more distinctly from the odontoid ; in some indi- 
viduals (or perhaps species) this separation is by means of a well-defined 
sulcus on each side of the process. (3) The centrum has a more distinct 
ventral keel and a rather more concave posterior face. (4) The neural 
