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AUG 10 1900 



IX. 071 Fossil and Recent Lagomorpha. By C. I. Forsyth Major, M.D. 

 [Communicated hy Prof. G. B. Howes, ^ec. Linn. Soc.) 



(Plates 36-39.) 



Head 16th June, 1898. 



Tooth-change and Tooth-formula in the Lagomyid.e. 



1 HE three extinct Lagomyidoe, Titanomys, Prolagus, and Lagopsis, and the surviving 

 Lagomys, have five nppev cheek-teeth, as against six in Leporidfe [Palceolagus and 

 Lepus s. 1.). From a comparison of the form and relative size of the teeth in Lepus and 

 Lagomys, the type genera of l)otli groups, Waterhouse * and Gervais f had rightly argued 

 that the last uj^per molar of Lagomys corresponds to the penultimate upper molar in the 

 Hare. Since Lepus changes the three anterior of the upper six, and the two anterior of 

 the lower five cheek-teeth, the formula heing therefore P.^, M.^, it might have been 



further inferred that the number of premolars in Lagomyidae is the same as in the 

 Lejioridfe. 



Curiously enough, in recent species of Lagomys the tooth-change has never been 

 examined. In 1870 J, O. Fraas described and figured the milk-dentition of Prolagus, 

 with J cheek-teeth, there being three deciduous molars above and two below. The 

 obvious inference is that the premolars are the same in number as the milk-teeth, and 

 therefore in agreement with what is known iu Lepus. 



Fraas, however, proposes quite a novel definition of what we have to consider to be 

 premolars, with the vmavoidable result of thus introducing an element of confusion. 

 Finding the three upper posterior and the three lower posterior cheek-teeth of Prolagus 

 more ia agreement as to general form with each other than with those anterior to them, 

 which are two in the ujiper and one in the lower jaw, he concludes that these last are to be 

 considered as premolars. According to this theory, which conflicts with the prior state- 

 ment of the number of deciduous teeth, the tooth-formula would be P. ^, M. tt. But 

 this second statement is again in flagrant contradiction with the following description of 

 the mode in which the tooth-change is supposed to occur. The anterior upper premolar, 

 termed P.^ by Fraas, is stated to have no deciduous predecessor, the place of the anterior 

 of the three deciduous teeth being taken by the premolar following behind the first, the so- 

 called P-i ; while the anterior premolar pierces the jaw in front of P.j and comes in place 



* Ci. E. Waterhouse, ' A Natural History of the ilammalia," vol. ii. p. 14 (1848). 

 t Zool. et Pal. Fraae., sec. ed. pp. 48, 49 (1859). 

 t Wiirttemb. naturw. Jahresh. xxvi. p. 169 (1S70). 

 SECOND SERIES. — ZOOLOGY, VOL. VII. 61 



