r length, 32.8
(31.9); breadth across zygomata, 24.2 (24.8); palato-frontal
depth, 15.0 (14.8); palatal length, 24.7 (24.1); length of
nasals, 12.7 (12.8); breadth of braincase, 18.1 (17.5);
breadth across mastoid processes of squamosals, 21.5 (21.4);
breadth of rostrum, 8.4 (8.1); length of rostrum, 16.9
(16.3); alveolar length of maxillary tooth-row, 9.3 (8.8);
breadth across angular processes of rami, 26.1 (26.2).

_Specimens examined._--Three, all from Jalisco, as follows:
4 mi. W Mazamitla, 2; 3 mi. WSW Mazamitla, 1.

_Remarks._--The features which distinguish _Pappogeomys alcorni_ seem
to be beyond the range of variation in _Pappogeomys bulleri_. In view
of the absolute quality of the differences between _P. alcorni_ and _P.
bulleri_, it seems best to regard the former as a species, rather than
as a subspecies of _P. bulleri_. Moreover, it seems unlikely that
actual intergradation of the two species can occur, since the broad,
low valleys between the higher terrain, where pocket gophers of this
genus are found, do not offer suitable habitat for _Pappogeomys_.

In every example of _P. bulleri_ that I have seen (more than 100
specimens, representing all of the named subspecies) the anterior
palatine foramina are long and slitlike and the nasals are always
narrow and emarginate posteriorly, whereas in _P. alcorni_ the anterior
palatine foramina are short and round and the nasals broad and squarely
truncate posteriorly. The conspicuous nasal patch of _P. alcorni_ is
large and bright cinnamon or buffy, and, although the nasal patch may
be large in some subspecies of _P. bulleri_, in each specimen
possessing the patch the hairs are whitish with little or no trace of
pigmentation.

One of the most interesting features of _P. alcorni_ is the reduction
of enamel on the posterior wall of the first upper molar. In _P.
alcorni_ the enamel present is thick, but it occurs only on the inner
one-fourth of the posterior wall of the tooth. The enamel is always
complete in _P. bulleri_; but in some old individuals it becomes thin
with wear, and at a casual glance may appear to be partly or entirely
absent. Close examination under magnification reveals, however, in
every specimen of _P. bulleri_, a fine line of enamel completely across
the posterior wall. It seems that the posterior enamel plate of M1 is
disappearing in both _P. bulleri_ and _P. alcorni_. In both species
the enamel on