1892.] MR. O. THOMAS ON THE GENTJS ECHINOPS. 503 



Passing now to the dentition of Centetes^, 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 stated^ 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 

 Otoci/on 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 my finding the minute calcified germ of m^ behind the ^ 

 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 m^, like our own " wisdom tooth," 

 long behind m^ 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^rs^ of the molars to disappear. For in one extremely aged 

 specimen, in which the molars and premolars are worn down to 

 the roots', m* has again entirely disappeared, and has evidently been 

 worn down and dropped out in the natural course of existence. 



' Thanks to the kindness of Prof. A. Milne-Edwards, who has sent me a 

 complete copy of the chapter referring to the Tanrecs in Geoffrey's rare 

 ' Catalogue du Musee,' I am 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 sj-nonymous 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 me of Geoffrey'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. Mamm. (2) 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. 



^ Mon. Insectiv. p. 69, pi. vii. fig. 7. 



^ 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^ has formed two, 

 and its p" three minute " teeth," these being of course merely the roots of 

 the proper teeth (see my own remarks, t, e, p. 311). 



