om _Dipodomys ordii sennetti_ (J.A. Allen) of the
mainland, _D. o. largus_ differs in: Color paler on pigmented areas;
white areas more extensive; skull averaging smaller except in basilar
length and length of nasals which are approximately the same as in _D.
o. sennetti_. From _Dipodomys ordii compactus_ True of Padre Island, _D.
o. largus_ differs in: Body longer; tail shorter; skull narrower across
tympanic bullae and across maxillary processes of zygomatic arches;
nasals shorter. From _Dipodomys ordii parvabullatus_ of the coastal
island south of Padre Island, along the gulf coast of Tamaulipas, _D. o.
largus_ differs in: Body and tail longer; basilar length of skull
averaging less; breadth across maxillary processes of zygomatic arches
greater; premaxillae not extending so far behind nasals.

_Remarks._--_D. o. largus_ resembles _D. o. compactus_ in external
proportions and _D. o. parvabullatus_ in cranial proportions. The degree
of difference between _D. o. compactus_ and _D. o. largus_ is less than
between _D. o. compactus_ and _D. o. parvabullatus_. To me, the three
subspecies mentioned in the preceding sentence are indistinguishable in
color.

Two of the eleven specimens of _D. o. largus_ are of the light color
phase (upper parts Cartridge Buff) whereas all but two of the eleven
specimens of _D. o. compactus_ are of the light color phase. Each of the
cheek-teeth of the upper jaw of _D. o. largus_ has a complete ring of
enamel around the dentine of the occlusal surface, as described by
Setzer (Univ. Kansas Publ., Mus. Nat. Hist., 1:517, December 27, 1949)
for _D. o. compactus_. The upper dentitions of ten specimens of _D. o.
compactus_ examined by me in this respect reveal a total of only five
teeth (in four individual animals) that have the enamel ring incomplete;
one premolar and three molars are incomplete on the lingual side and one
molar is incomplete on the labial side.

Two specimens from Bagdad, Tamaulipas, in the delta of the Rio Grande
(Nos. 116485 and 11487, U.S.N.M., Biol. Surv. Coll.), are referred to
_D. o. compactus_ on basis of long body and long tail. The specimens,
both Light Ochraceous-Buff, are so young that not all of the enamel is
worn off the crowns of the cheek-teeth. Specimens of _D. o. compactus_,
_D. o. parvabullatus_ and _D. o. sennetti_ of comparable age are not
available, and it, therefore, is impossible to know whether size and
shape of the skull in the population at Bagdad are t