While examining lately the magnificent collection of fossil musk-deer, from Auvergne, in the collection of the British Museum, in the case devoted to the specimens collected by M. Bravard from the lacustrine calcareous marls of Puy-de-Dôme, a singular anomaly in the structure of the crania of the genus Cainotherium met my view. All the writers who have described the osteology of the skull of Ruminants have noticed those singular deficiencies or lacunæ which exist at the points of junction of the various bones, and which have been variously described as “lacrymal openings” or “facial interspaces.” Their function has been unknown, and their presence, although constant in each individual species, is variable in species nearly allied to each other. In the Cainotherium commune, Bravard (Microtherium Renggeri), nearest allied to the Hyomoschus of the present day, ossification at this lacrymal point of intersection has extended to a much less degree than in its living analogue. The interspace in Cainotherium is longer in proportion to its breadth than the existing musk-deer (Moschus chrysogaster). In the Dorcatherium Naui, Kaup., on the contrary, not the slightest interspace is exhibited, and the lacrymal angle is definitively closed: In some of the specimens named Cainotherium in the British Museum, no interspace exists. These probably belong to a separate species, as De Blainville remarks on the typical Cainotherium commune, termed by him Anoplotherium laticurvatum, that it possesses “des lacunes sous-lacrymales assez grandes, en forme de longues virgules.”