270 
The American Geologist, 
m: ay, 189 6' 
.Comparing the diameters of both pm and pm we find first, that 
in pm the transverse and antero-posterior diameters are twice 
those in the type species, while in pm the antero-posterior is 
less than twice and the transverse diameter equal to that of 
the type. Again, pm of T. wallovianus (the smallest species- 
of the three) has a greater antero-posterior diameter than T. 
altigenis , and further, in pm of the same species the diameters 
are slightly greater than and in the still smaller species, 
josephi (No. 1, p. 912), nearly equal those in the type species- 
The contour of the crown of pm in T.ferox is of a regular 
rectangular shape and compressed transversely, while in 1 \.. 
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. Pm 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; 7\ altigenis and IT 
wallovianus have nearly the same measurements, indicating; 
for the smallest species the greatest relative development. In 
T.ferox a minute cusp (1.5mm.) is developed on this tooth r 
but is absent in the other species. T.ferox and T. wallovia¬ 
nus have their greatest transverse diameter at the posterior- 
while in T. 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 pm do not conform 
to *hose ( 0 the preceding premolars. In T.ferox and T. alti¬ 
genis the diameters across the deutero- and tritocones are 
(and in T. 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 T. al¬ 
tigenis and T. 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), T. 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; 
