Mr. E. D. Cope on the Bunotherian Mammalia. 25 
thertum, where the external cusps are present. Centetes and 
Chrysochloris only differ from these in that the internal cusps 
are wanting. In addition, the latter genus presents a rudi- 
ment of the posterior inner tubercle, as is seen in Deltathertum. 
An explanation similar to this is admitted by Mr. Mivart to 
apply to the cusps of the inferior molar of Centetes. It remains 
to ascertain whether the cusp in this genus, Chrysochloris, &c. 
represents an intermediate or not. 
Secondly, as regards the Talpide and Soricide, where the 
external V’s are well marked. If we examine the external 
cusps in the genus Didelphys, we find that the posterior one 
becomes gradually more anterior in its position, until on the 
second true molar it stands largely above the interspace be- 
tween the roots instead of over the posterior root. It will also 
be seen that the anterior intermediate tubercle is distinct and 
of insignificant proportions, while the posterior intermediate is 
large and is related to the posterior external as is the apex of 
a V to its anterior base. In this arrangement I conceive that 
we have an explanation of the V’s of the Talpide and Sori- 
cide. The first true molar of Scalops is a good deal like that 
of Didelphys; but the anterior cusp is larger and there is no 
anterior intermediate cusp, while the posterior external is of 
reduced size. ‘The posterior V is better developed than in 
Didelphys but is composed, in the same way, of a posterior 
intermediate cusp, and a posterior external with a posterior 
heel. ‘These are united by stronger ridges in Scalops, Con- 
dylura, and Blarina than m Didelphys. On the second true 
molar in Scalops a V represents the anterior external cusp of 
the first true molar. Whether this V has a constitution like 
the posterior one, 7. e. is composed of external and intermediate 
cusps joined, is difficult to determine; but it is probably so 
constituted. It seems to be pretty clearly the case in Blarina, 
where the fourth premolar and first true molar may be com- 
pared, with a resulting demonstration of the correctness of 
this view. In Condylura the V’s have become more deve- 
loped and the external cusps reduced, so that the analysis is 
more difficult. 
This interpretation applied to Urotrichus and Galeopithecus 
gives them quadrituberculate molars, not trituberculate, as 
determined by Mivart. Mystomys is tritubercular. The 
intermediate tubercles are present, but are imperfectly connected 
with the external, so that V’s are not developed (wide figures 
of Mivart and Allman). This genus offers as much confirma- 
tion of the homology here proposed as do the opossums; but 
it differs from the latter in having the anterior intermediate 
tubercle the larger, instead of the posterior, Mystomys and 
