_Diagnosis._--Size large (see measurements); tail short; hind foot large; upper parts Fuscous-Black, strongly mixed with Walnut Brown, underparts Cinnamon-Buff, bases of all hairs Plumbeous; skull large, broad, rugose; outline of dorsal profile slightly concave, almost flat; zygomata strongly constructed, maxillary arm almost touching squamosal arm over jugal; wide across zygomata; nasals actually and relatively long; rostrum relatively narrow; auditory bullae inflated, relatively large; maxillary teeth relatively large. _Comparisons._--From topotypes of _C. z. zinseri_ from Lagos, Jalisco, _C. z. morulus_ differs in: Tail shorter (averaging 96 in females compared with 101, 94 in males compared with 115); color darker above, Fuscous-Black instead of Cinnamon-Rufous, underparts paler; skull larger (occipitonasal length 63.7 rather than averaging 58.5 in females and 68.6 rather than 63.1 in males); wide across zygomata; nasals actually and relatively longer; rostrum relatively narrower; wider across mastoid processes of squamosal; auditory bullae inflated, relatively larger; maxillary teeth larger. From _C. z. zodius_, that occurs to the northeast, _C. z. morulus_ differs in: Body larger (see measurements); hind foot larger; color of upper parts darker, underparts paler; skull much larger, broader, more rugose; dorsal profile of skull slightly concave rather than convex; wider across zygomata; nasals actually and relatively longer; rostrum broader, more massive; wider across mastoid processes of squamosal; auditory bullae larger; maxillary teeth larger. _Measurements._--The type and an adult female (her measurements in parentheses) from the type locality measure: Total length, 358 (338); length of tail, 94 (97); length of hind foot, 49 (45); occipitonasal length of skull, 68.6 (63.7); basilar length, 58.0 (55.6); zygomatic breadth, 49.3 (45.0); interorbital breadth, 9.6 (8.9); greatest height of cranium, as explained above, 26.1 (24.6); least depth of rostrum, 12.5 (10.8); breadth of rostrum, 14.5 (13.7); length of nasals, 25.9 (22.5); width across mastoid processes of squamosal, 47.7 (42.8); height of occiput, 19.8 (17.8); length of maxillary tooth-row, 13.9 (13.8). _Remarks._--_Cratogeomys zinseri morulus_ is the darkest subspecies known of _C. zinseri_. It differs widely from other subspecies of this species in color and the large size of the skull.