At the lateral edge of the enamel plate of the incisors there is a
distinct shelf, a characteristic of the _merriami_ group of species and
a feature not well developed in _Cratogeomys castanops_.

I hestitate to refer this fragment to any of the living species,
although I would judge it to represent a form closer to the species
_castanops_ than to the _merriami_ group (_C. perotensis_). The rostrum
may represent, and probably does, an undescribed and extinct species of
_Cratogeomys_, but in my opinion it should not be given formal taxonomic
status until more adequate material is available.

If the fossil is actually _Cratogeomys castanops_, and if the fragment
is from an earlier deposit in the cave than is the material here
assigned to _Cratogeomys castanops_, the fossil stock could be ancestral
to the group of small subspecies provided there had been a trend in
evolution toward smaller size. Another possibility is that a shift in
geographic range of the kinds of _Cratogeomys_ that lived in the
vicinity of the cave has occurred, and that the fossil represents an
evolutionary line with no close relationship to Recent species and now
is extinct. Additional material is needed before the history of these
species can be reconstructed with validity.

#Heterogeomys onerosus# new species

_Holotype._--Los Angeles County Museum (C.I.T.) No. 2384, an
incomplete left ramus, bearing incisor and p4; the alveolus of
m1-m3 is present (Fig. 1a). Paratypes: Two isolated and unnumbered
right upper incisors, one isolated premolar, and five additional
rami, Nos. 2385, 2386, 2388, and two with no number.

_Horizon and type locality._--Upper Pleistocene, Cueva de San
Josecito, province of Aramberri, near the town of Aramberri, Nuevo
Leon, Mexico; California Institute of Technology, Vertebrate
Paleontology Locality 192.

_Description of Holotype._--Differs from any known living species of
_Heterogeomys_, by the significantly heavier and deeper ramus (see Table
1 and Fig. 1). The holotype is compared with the largest adult male of
_Heterogeomys hispidus_ (_H. torridus_ is smaller than _hispidus_)
available to me in Table 1. Relative to the length of the ramus
(measured from the anterior mental foramen to the posterior margin of
the capsule that surrounds the root of the lower incisor), the depth of
the ramus anterior to the molariform tooth-row is 33.0 per cent in _H.
onerosus_ compared with 27.3 per cent in