Holotype.—Cranium, lacking post-incisor dentition on the left side, zygomatic arches and auditory bullae; Los Angeles County Museum (CIT) No. 3129; from Pleistocene deposits of San Josecito Cave, near Aramberri, Nuevo León, México.

Referred material.—Twelve additional partial crania, LACM (CIT) 2946-50, 3127-30, 3940-41, 2 unnumbered.

Diagnosis.—Resembling the Recent Desmodus rotundus but differing from it as follows: Skull larger (see measurements and Figs. 1-2), heavier and more massive; rostrum and braincase relatively as well as actually broader, interorbital region relatively more constricted; braincase more rounded (less elongate) as viewed from above; nasals less concave in lateral view; narial vacuity broader in relation to greatest length of skull, more nearly heart-shaped; palate broad, less concave medially; mesopterygoid fossa relatively and actually broader anteriorly, the sides nearly parallel; zygomatic arches (judging from No. 2950, the only specimen with a complete arch, the left) less rounded in outline, appearing broader owing to the more constricted interorbital region.

Dentition larger and heavier than that in rotundus, but otherwise differing only slightly from it; upper incisor less concave on cutting surface (see Figs. 3-4); premolar and molar slightly less bladelike, with heavier roots.

The peculiar shape of the incisor of stocki is shared to some extent with Diaemus youngi, a Recent South American desmodontid. However, stocki does not otherwise resemble D. youngi, differing from it as follows: Skull larger and heavier; interorbital constriction much narrower; zygomatic arches less strongly bowed; skull less compact, more elongate; braincase and rostrum relatively much narrower in relation to greatest length of skull. Furthermore, specimens of stocki show no trace of the minute M2 attributed to youngi by de la Torre (Proc. Biol. Soc. Washington, 69: 191, 1956). For cranial measurements of youngi see Sanborn (Jour. Mamm., 30: 283, 1949).