FOSSIL AND KECENT LAGOMOKPHA. 483 



encore, comme sous-^enre, par la derniere molaire inferieure, qui a trois prismes par 

 reunion de la cinquicme molaire a la quatrieme " *. Eraas holds the same opinion f. 



This theory would at first sight seem to be supported by what Dei)erct has found 

 in the ProIagKS of Roussillon. He figures two mandibular rami '^, in one § of 

 which he records five cheek-teeth, in the other 1| only four ; and he goes on to say : — 

 " Cette dilFeronce est moins importante qu'elle ne pent sembler au premier abord ; 

 elle tient simplement a ce que le dernier prisme d'email de la serie dentaire est soude 

 au prisme jirecedent de la quatrieme molaire dans I'une de ces mandibules, tandis que 

 ce meme prisme libre constitue une cinquieme molaire dans la fig. 29. Cette soudure, 

 qui se fait d'ailleiirs uniquement par I'intermediaire d'une certaine quantite de cement, 

 ne me parait pas avoir I'importance qu'on lui a attribuee pour la distinction des deux 

 genres Lacjomys et Frolagus, puisqu'elle est variable suivaut les sujets dans le petit 

 Leporide de E,oussillon " ^. 



I agree witli Prof. Deperet that this difference has no great importance in the E-oussillon 

 jaws, though not for the reasons adduced, for I apprehend he is mistaken when he 

 institutes comparisons with Lacjomys, and considers that the isolated prism of his 

 fig. 29 " constitue une cinquieme molaire." H. v. Meyer met with similar occm-- 

 rences among twenty mandibular rami of Frolagus oenmgensis (Kon.) from Steinheim, 

 and refers to them in the following words : — " In some instances one might be induced 

 to believe that the posterior of the three prisms constituting the last molar is separated, 

 so that the creature would have the character of Lagomys " ; but he judiciously 

 adds : — " On closer examination, however, it can be seen that tlie posterior prism is 

 included in the alveolus of the rest of the tooth, so that it evidently is part of the 

 latter " (" dass das hinterste Prisma nicht durch die Alveole von dem iibrigeu Zahu 

 abgeschlossen ist, zu dem es daher offenbar noch gehort) " **. Numerous mandibular 

 rami of the Frolagus ceii'mgensis from La Grive have passed through my hands, as well 

 as from 600 to 700 of F. sardus from the Corsican and Sardinian ossiferous breccias and 

 caves. Not unfrequently I foimd the third prism of m. 2 separated from the rest of 

 the tooth ; but by the criterion established by H. v. Meyer there could never be a doubt 

 as to the interpretation, which invariably was that, either by fracture or by the weathered 

 condition of the cement, the last prism had been separated from m. 2 ; as are likewise, 

 though more rarely, separated from each other the two prisms of the aiaterior teeth. 

 I do not doubt for a moment that the same explanation will hold good in the case of 

 the E-oussillon specimens. In Frolagus each of the prisms has its alveolar niche 

 formed by two partial septa starting from the outer and inner alveolar border ; but these 

 must not be confused witli the complete septum separating one alveolus from the 

 other. 



I consider the tliird prism of ni72 of Frolagus to be the homologue of t of the 



* Cat. meth. et desor. Vert. toss, du Bassiu de la Loire et de I'Allier, p. 43 (1853). 

 t Wiirttemb. naturw. Jahresh. xxvi. p. 170 (1870). 



% " Aiiim. plioo. du Koussillon," Mem. Soc. Geol. France, i. p. 57, pi. iv. (1890). 

 § Op. tit. pi. iv. figs. 2iJ, 29 a. 



II Oj}. cit. pi. iv. figs. 28, 28 a. f Oi>. dt. p. 57. ** Neiies Jahrb. 1865. p. 8t3. 



67* 



