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Show 1904.] PECULIARITIES IN CERTAIN MAMMALS. 417 In all the genera of Hystricidae we have normally four cheekteeth above and below on either side of the jaw, making sixteen in all. Of these, the three posterior are true molars; the anterior Text-fig. 79. Hystrix leucura, left maxillary. Double nat. size. one of each row is, in Hystrix, a premolar, having replaced a deciduous tooth. The four teeth of the species of Hystrix are Uber die sogenannten Leporiden, p. 15,1876).-An adult rabbit's skull, now before me, containing two left posterior incisors, situated side by side, was exhibited some years ago at a meeting of this Society by Mr. Holding.-Complete absence of the small posterior incisors, without any trace suggesting that they had ever been present, was met with by H . v. Nathusius in the skull of a so-called " Leporide," forwarded to him as the presumed descendant of a cross-breed between the Rabbit and the C o m m o n Hare. The same writer records a communication to him from Hensel, who had found that these posterior incisors were absent in several skulls of the common domestic rabbit (Der Zoologische Garten, xx. p. 134, footnote (1879)).- The last upper molar in Leporidae, being much reduced, might be expected to be frequently missing; it is, however, remarkably constant. G. R. Waterhouse mentions a case in a " Lepus tnediterraneus " where this sixth upper molar was absent on either side ('A Natural History of the Mammalia,' ii. p. 44 (1848)). Although it has been repeatedly asserted (Ann. Mag. Nat. Hist. (3) xx. p. 222 [1867] ; (7) i. p. 157 [1898]) that Waterhouse was mistaken in making this statement, he was perfectly right; the skull in question, from the Island of Kerkenna, off Tunis, is in the British Museum (Zool. Dep.), No. 46.10.30.162. ? . At m y request, Mr. 0. Thomas was good enough to have the skull taken out of a second hare's skin from Kerkenna, No. 46. 10.30.161, and in this also the last upper molar is absent on both sides ; in the case of the Kerkenna Hare it seems therefore that we have to do with something more than a mere individual variation. It would be interesting to ascertain whether this character is constant in the Kerkenna Hare, which differs besides from the one on the neighbouring continent (Lepus tunetee de Wint.), with which it was united by previous writers, in the much larger size of the cheek-teeth and incisors, as well as in other characters.-The only other specimen of a Lepus in the Natural History Museum showing the anomaty referred to, is a skull of a $ of Lepus europaus occidentalis, from Merton Hall, Norfolk (No. 98.2.11.1); on the left side the last upper molar is present, but there is no trace of either the tooth or its alveolus on the right side.-In Caprolagus hispidus (Pears.), the Assam Hispid Hare, the last molar is more reduced in size than in any other member of the Leporidae; but is missing in none of the five skulls of the species in the Natural History Museum. A second species of Caprolagus, C.fumessi Stone, obtained on the Liu Kiu Islands, was described not long ago ; in the only skull examined there was " no trace whatever of the small posterior upper molar" (Proc. Ac. Nat. Sci. Philad., 1900, p. 461). |