large as, or perhaps larger than, the holotype, although the posterior part of the ramus behind the alveolus of m2 is missing. An additional unnumbered ramus is of somewhat lighter construction than the holotype, but is important since it bears not only the incisor and p4 but also the first two lower molars. The only other material referable to Heterogeomys onerosus is a fragmentary and isolated lower molar tooth that has a single posterior enamel blade, a feature characteristic of a number of Recent genera of pocket gophers, and some limb bones which are slightly larger than corresponding elements in Recent species of Heterogeomys.

Remarks.—Pocket gophers do not inhabit caves; therefore gophers were brought into the cavern probably by birds of prey, the remains of which were common in the deposits (Miller, 1943:152-156), or conceivably by carnivorous mammals. Since most of the raptorial predators that would prey on pocket gophers do not have a wide hunting territory, it is likely that the gophers were taken within a short distance of the cave. The presence of the genus Heterogeomys in the deposits strongly suggests a tropical situation in the vicinity of the cave when these gophers were taken, because the distribution of this genus today is entirely within the Tropical Life-zone.

Since the presumably early time when tropical conditions, or more nearly tropical conditions, prevailed at San Josecito Cave, climatic shifts account for a humid boreal environment there and its associated fauna. Findley (lit. cit.:635-636) reports from San Josecito the remains of the boreal shrew Sorex cinereus that today occurs no nearer than 800 miles to the northward in the mountains of north-central New Mexico. As he points out, that species requires hydric communities of cool climates, and in the Wisconsin Glacial age such climates probably prevailed in the high mountainous region where San Josecito is located. Since the time when a more mesic boreal environment occurred at San Josecito, climatic shifts have favored more xeric conditions as are found in the vicinity of the cave today. The more arid environments would support the occurrence of Cratogeomys and Thomomys; however the ecological affinities of the fragment here referred to Cratogeomys sp. are unknown.

The more nearly tropical environment there could have occurred either during a Wisconsin interglacial period or during the Sangamon Interglacial age. Heterogeomys onerosus perhaps lived near the cave during an interglacial period; since then it became extinct or evolved into the Recent species Heterogeomys hispidus. Heterogeomys has not previously been recorded from Pleistocene or earlier deposits.

Baker, R. H.

Cushing, J. E., Jr.

Findley, J. S.

Handley, C. O., Jr.

Hooper, E. T.

Jakway, G. E.