_H. hispidus_. If the fossil
ramus is that of a female (females are significantly smaller than males
in _Heterogeomys_) then the differences would be greater than recorded.

TABLE 1. DEPTH OF MANDIBULAR RAMUS

A: Least depth in front of premolar
(See A to A' on Fig. 1c)
B: Depth of ramus opposite re-entrant angle of p4
(B to B' on Fig. 1c)
C: Depth from a point in front of capsule for incisor
(See C to C' on Fig. 1c)

=====================================+======+======+======
| A | B | C
-------------------------------------+------+------+------
_H. onerosus_ holotype | 11.0 | 17.4 | 11.7
-------------------------------------+------+------+------
_H. h. hispidus_ [Male] ad., 23979 KU| 9.1 | 15.2 | 10.5
-------------------------------------+------+------+------

The angle between the anterior border of the coronoid process and the
dorsal border of the ramus of the mandible is more acute, and the
posteroventral margin of the ramus is more nearly straight, in
_onerosus_ than in _hispidus_. The molariform tooth-row in _onerosus_ is
only slightly longer (13.9 in contrast to 13.5) than in _hispidus_ and
_torridus_. The ventral border of the massenteric ridge is weakly
developed in _onerosus_ and hardly discernable whereas in the living
species of _Heterogeomys_ the massenteric ridge is strongly developed
posteriorly forming a noticeable prominence.

_Description of Paratypes._--The fossils are referable to the genus
_Heterogeomys_ on the basis of the short lateral angular processes of
the lower jaw and on the basis of the associated upper incisors, which
have a single distinct sulcus that lies toward the inner margin of each
tooth. The isolated lower premolar that is referred to the new species
is as large as that of the holotype and has the enamel pattern of
_Heterogeomys_.

[Illustration: Figs. 1a-1c. x 1-1/2

FIG. 1a. _Heterogeomys onerosus_, lateral view of left lower jaw of
holotype.

FIG. 1b. _Heterogeomys onerosus_, front view of right, upper incisor.

FIG. 1c. _Heterogeomys hispidus_, lateral view of left lower jaw, No.
23979, [Male] adult, from 3 km. E San Andres Tuxtla, Veracruz.]

One jaw fragment, L.A.C.M. (C.I.T.) No. 2368, is smaller than the others
and probably is from a young individual. Two others L.A.C.M. (C.I.T.)
No. 2384 and one unnumbered, are smaller than the holotype, and possibly
are the remains of females; however, the