1904.] 



PECULIARITIES IN CERTAIN MAMMALS. 



417 



In all the genera of Hystricidse we have normalty foui' cheek- 

 teeth above and below on either side of the jaw, making sixteen in 

 all. Of these, the three posterior are true molars ; the anterior 



Hystrix leucura, left maxillaiy. Double iiat. size. 



one of each row is, in Hystrix, a premolar, having replaced a 

 deciduous tooth. The four teeth of the species of Hystrix are 



tjber 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 Eabbit 

 and the Common 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 Leporidic, being much reduced, might be expected to be 

 frequentlj' missing ; it is, however, remarkablj' constant. G. R. Waterhouse mentions 

 a case in a. " Lepus mediterranmis " wh&ce 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 my 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 timefee 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 anomaly refeiTed to, is a skull of a $ of Lepus europeeus 

 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.fu,rnessi Stone, obtained on the Liu Kiu Islands, 

 was described not long ago ; in the only skull examined there was " no trace what- 

 ever of the small posterior upper molar " (Proc. Ac. Nat. Sci. Philad., 1900, p. 461). 



