C. laticurvatum: head large, especially towards the frontals, with a straight profile as far as under the orbits, depressed towards the fronto-parietal surface.
C. commune (= C. latecurvatum, De Blainville): smaller; head more lengthened, and more elevated towards the parietal region.
C. elegans: of the size of the preceding: head still more convex towards the fronto-parietal suture: palatines more sloping: limbs more slender.
C. metapium (? etopium, from , μετώπιον, forehead): size of the preceding; head more concave in front of the orbits; forehead consequently more elevated; zygomatic arch very short.
C. gracile: one-third smaller; mandibular bone very narrow, symphysis shorter, more projecting beneath; limb-bones very short.
I have recently made a careful examination of the Cainotheria in the British Museum, where M. Bravard's and M. Pomel's specimens are deposited, with a view to detect any specific differences which might be visible. I have not had the opportunity of knowing on which specimens M. Pomel's conclusions were founded. I merely record my conviction that the British Museum collection does not contain more than two species at most, the Cainotherium commune and C. metapium, if the specific distinction of the latter species is to be admitted. Some of the specimens in the British Museum collection are named C. majus by M. Pomel. Another, apparently not specifically distinct from the C. commune, M. Bravard terms C. lepthelicium. One of the Museum specimens, by the degree of concavity or depression of the preorbital space, may belong to the C. metapium of Pomel, but this is very doubtful. No dental distinction has been detected by me, even though aided by a strong lens. The few slight differences which otherwise exist are merely referable to age. The degree of backward inflection of the coronoid process of the jaw varies, so to a less extent do the proportions of the limb-bones, but not more so than between the skulls of musk-deer at various ages.
The generic name Microtherium must clearly give place to Cainotherium, which was invented two years earlier. Of the identity of the species there can be no doubt. The specimen of Microtherium Renggeri in the British Museum, from the Miocene of Haslach, in Wurtemberg, being the right upper maxillary, with m 3 coming into place, is in no manner specifically distinct from the Cainotheria from Allier, in the same case.
Whether the genus Hyægulus of Pomel rests upon a correct appreciation of its generic value, may be much doubted. The mere fact of the scaphoid and cuboid bones being confluent would scarcely merit generic distinction, and the alleged deeper sculpturing of the hinder molars in Hyægulus murinus is far from visible on M. Gervais' plate. The teeth of Cainotherium Courtoisii might very well belong to the young of Cainotherium commune, before the molars have been abraded by use. The abrasion of the molars in some of the Museum specimens might lead a hasty species-maker to form several species.
None but the practical worker can appreciate the difficulty of
