27<> The American Geologist. May, 189.S 
( Jomparing the diameters of both pj and p. 2 we find first, thai 
in p. 1 the transverse and antero-posterior diameters arc twice 
those in the type species, while in p. 2 the antero-posterior is 
less than twice and the transverse diameter equal to that of 
the type. Again, p. 2 of '/'. wallovianus (the smallest species 
of the three) has a greater antero-posterior diameter than T. 
altigenis, and further, in i^j of the same species the diameters 
are slightly greater than and in the still smaller species. '/'. 
josephi (No. 1. p. 912), nearly e<pial those in the type species. 
The contour of the crown of vri in T.ferox is of a regular 
rectangular shape and compressed transversely, while in T. 
altigenis the external and internal lines are so formed as to 
produce nearly an L-shape, the point of divergence being the 
cone from which the anterior edge comes forward and the 
posterior outward. I\3 exhibits the same irregular variation 
in size; in T.ferox. it has, perhaps, a slightly greater antero- 
posterior diameter and the transverse diameter is one-half 
that of the antero-posterior, while in the type this diameter is 
less than one-third the antero-posterior; T. altigenis and T. 
wallovianus have nearly the same measure-nients, indicating 
for the smallest species the greatest relative development. In 
T. ferox a minute cusp (1.5 mm.) is developed on this tooth, 
but is absent in the other species. 1'. ferox and /'. wallovia- 
nus have their greatest transverse diameter at the posterior, 
while in 7'. altigenis it is greatest at the anterior. This is due 
in a measure to the position of the main cone, rising as it 
does, at the anterior, in the latter species and at the centre, in 
the former. The irregular variations in p^j do not conform 
to 1 hose < e the preceding premolars. In T.ferox and 7'. alti- 
genis u.t- diameters across the deutero- and tritocones are 
(and in 7'. wallovianus, nearly) equal. The proto-tritocone 
diameter is slightly greater in the type species and the trans- 
verse or proto-deuterocone diameters are equal in both 7'. al- 
tigenis and 7'. wallovianus and one-fourth greater in T.ferox. 
From this may be deduced the fact that the largest species- 
has the least (or smallest) development. As mentioned above, 
the smallest species (of the three), 7'. wallovianus, seems to 
have, proportionately, the greatest development in the premo- 
lar series. In the species under consideration, T. ferox. the 
protocone has the greatest height, the anterior edge inclines 
