convex
in dorsal outline; zygomata widely flaring; palate short; rostrum
short; nasals short; mastoid and tympanic bullae inflated;
basioccipital with lateral edges parallel; maxillary teeth small.

_Comparisons._--From _Cratogeomys castanops convexus_, found to the
north, _bullatus_ differs in: Hind foot shorter; skull much broader in
relation to length; rostrum narrower but, relative to length of skull,
wider; tympanic bullae slightly more inflated; incisors and maxillary
teeth smaller. From topotypes of _Cratogeomys castanops angusticeps_,
found across the Rio Grande and upstream from localities where
_bullatus_ is known to occur, _bullatus_ differs in: Body slightly
smaller; color paler, especially on sides; skull shorter and broader;
rostrum shorter and broader; nasals shorter; mastoid and tympanic
bullae more inflated; maxillary teeth smaller. For comparisons of
_bullatus_ with the subspecies of _C. castanops_ found to the west and
south, see accounts of the subspecies to follow.

_Remarks._--_Cratogeomys castanops bullatus_ in small size resembles
_C. c. tamaulipensis_ Nelson and Goldman of the lower Rio Grande
Valley in Tamaulipas, but the two differ markedly in cranial features.
_Cratogeomys c. bullatus_ is smaller than _convexus_ but these two
subspecies resemble each other in color and cranial characters. Both
have an arched skull, inflated mastoid and tympanic bullae, short
nasals, and a short rostrum. Comparison of _bullatus_ with
_angusticeps_, which occurs across the Rio Grande but not directly
opposite the range of _bullatus_, indicates that these two subspecies
are less closely related than _bullatus_ is to _tamaulipensis_ and
_convexus_.

_Cratogeomys castanops bullatus_ is especially common in sandy
soils in the vicinity of Nava where the mounds were in fallow
irrigated fields and other open places between extensive live oak
thickets. South and west of the Rio Grande the animals were less
abundant and lived in heavier soils usually as individuals or in small
groups. Specimens were taken at elevations from as low as 800 feet to
as high as 2,000 feet.

_Specimens examined._--Total, 24, from: 2 mi. S and 6-1/2 mi. E Nava,
810 ft., 2; 2 mi. S and 12 mi. E Nava, 800 ft., 1; _3 mi. S and 12 mi.
E Nava, 800 ft._, 4; 29 mi. N and 6 mi. E Sabinas, 5; 10 mi. E
Hacienda La Mariposa, 2000 ft., 1; La Gacha [= La Concha], 1600 ft.,
8; 8 mi. S and 8 mi. E Hacienda La Mariposa, 1900 ft., 1; 9 mi. S and
11 mi. E