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Show 1892.] MR. O. THOMAS ON THE GENUS ECHINOPS. 503 Passing now to the dentition of Centetes1, besides the known increase by one each in the number of the upper milk and the lower milk and permanent incisors, we find a most remarkable and noteworthy character in the number of the molars. When writing his invaluable Monograph of the Insectivora, Dr. Dobson stated2 en passant, and merely as a question of specific difference or identity, that certain specimens of Centetes ecaudatus in the British Museum were much larger than usual, and had an additional upper molar. Now remembering the continual and unending discussion that the presence of four true molars in Otocyon has given rise to, it is evident that the occurrence of a fourth upper molar in Centetes is an exceedingly interesting fact, and one that deserves to be brought into much greater prominence. A renewed examination of the specimens shows that the presence of four molars is not a merely accidental variation in one or two individuals, but is a normal character of the species, although the fourth molar only comes up very late in life-so late, in fact, that the great majority of Museum specimens do not possess it. This is proved by m y finding the minute calcified germ of m4 behind the Q^3 of what is, apart from the three unusually large individuals referred to by Dobson, the largest skull in the Museum collection, and one that, in the absence of these three, would have been put down as a remarkably fine and well-grown one. Judging, therefore, by the specimens in the Museum, it appears probable that the species seldom attains to the great age necessary to obtain the fourth molar, but that when it does, it normally has the additional tooth. Curiously, however, not only is m4, like our own " wisdom tooth," long behind m 3 in its date of appearance, but owing to the fact that it projects further into the mouth and is rather feebly attached, it is the first of the molars to disappear. For in one extremely aged specimen, in which the molars and premolars are worn down to the roots3, m 4 has again entirely disappeared, and has evidently been worn down and dropped out in tbe natural course of existence. 1 Thanks to the kindness of Prof. A. Milne-Edwards, who has sent m e a complete copy of the chapter referring to the Tanrecs in Geoffroy's rare ' Catalogue du Musee,' I a m most fortunately able to state that the name Setiger, Geoffr. (1803), need not displace Centetes, 111. (1811), a change which appeared to be imperative on reading Trouessart's paper, already quoted. In this paper, while stating that Setiger was absolutely synonymous with Centetes, the author exercised in favour of the latter that fancied right of selection which has been so disastrous throughout the history of zoological nomenclature. However, the copy now before m e of Geoffroy's words shows that the typical and first mentioned species of his genus " Setiger" is " S. inauris," whose characters are largely mixed up in the generic diagnosis; and this animal, as we know from p. 22 of Isidore Geoffroy's paper on the group (Guerin, Mag. Zool. M a m m . (-!) 1839, Art. 1), was neither more nor less than a common Hedgehog which had lost its ears. This being the case, Setiger becomes a synonym of Erinaceus, Linn., and happily remains in its time-honoured obscurity. 2 Mon. Insectiv. p. 69, pi. vii. fig. 7. 3 This specimen presents an example of that mechanical wearing down, and consequent increase in the number of "teeth," on which Dr. Kiikenthal in the case of a Seal has laid such stress (t. c. p. 367); for its p 2 has formed two, and its p 3 three minute " teeth," these being of course merely the roots of the proper teeth (see m y own remarks, t. c. p. 311). |
