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Show 402 MR. G. E. DOBSON ON THE HALLUX OF MAMMALS. [June 3, EXPLANATION OF THE PLATES. PLATE XXXIV. Fig. 1. Female hybrid bovine, B. Born May 21, 1881. 2. Female hybrid bovine, C. Born March 12, 1884; one month old. (Drawn April 14, 1884.) PLATE XXXV. Fig. 1. Female hybrid bovine, C. Born March 12, 1884; eleven weeks old (Drawn June 1, 1884.) 3. O n the Unimportance of the Presence or Absence of the Hallux as a Generic Character in Mammalogy, as show n by the gradual Disappearance of this Digit within the limits of a single Genus. By G. E. D O B S O N , M.A., F.R.S. [Received May 29, 1884.] The presence or absence of the hallux has been so often considered by mammalogists as sufficient ground for the formation of a new genus, that any instances in which it can be shown that this digit may disappear within the limits of a single genus, the species of which are united by indissoluble bonds of common affinity, is of much interest and importance. Of all the genera of Placental Mammals few exhibit such close affinities among the species composing them as Frinaceus, which may be taken as an example of a thoroughly natural genus incapable of division into subgenera or well-marked subdivisions of any kind. Nevertheless this genus has been divided, one species, E. albiventris, having formed the type not only of a new subgenus (Atelerix, Pomel), but even of a new genus (Peroechinus, Fitzinger). Although, as already pointed out in my ' Monograph of the Insectivora'1, I have long considered the absence of the hallux in E. albiventris of little importance, seeing that that digit presents all degrees of development in the other species, from its comparatively large size in E. europaus down to its rudimentary condition in E. diadematus, where it is only 4 m m . in length, yet, up to the time of writing this note, I was unable to find any examples in which the extent of development of this digit might be said to be truly intermediate between its condition in E. diadematus and E. albiventris. Lately, however, in a collection kindly made for m e at Lagos by the Colonial Surgeon, Dr. J. W . Rowland, I found specimens of E. albiventris (well preserved in alcohol), which furnish all the material required. The specimens referred to consist of examples of an adult female, in which the second upper premolars of both sides have already been HSRof MonoSraPb of the Insectivora, Systematic and Anatomical,' pt. i. |