FOSSIL AND EECENT LAGOMOEPHA. 



481 



Fig. 7, PI. 37, shows this tooth iu place in a left mandibiilar ramus of Tltmiomys 

 Fontanuesi. It is not a simple cylinder, as in Lagopsis and Lacjomijs, but is composed of 

 two lobes, a larger anterior one and a small posterior, attached to the former in the 

 same manner as in the anterior molars the terminal cusp {t) is attached to the lobe 

 preceding it, viz. separated from it by cement, only iu the upper part. Eor this 

 reason, and because the anterior lobe of m. 3 shows traces of greater complication, 

 1 homologize the posterior lobe of this tooth with t of the anterior molars ; the anterior 

 lobe of m. 3 would then represent hoth the principal lobes of the anterior molars. 



When discussing the tooth-formuhi of Tltanomijs, allusion was made to Filhol's 

 suggestion that the terminal cusp of m. 2 of T. visenoviensis might be the representative 

 of m. 3 of the recent Lagomys, in the specimens of the former where this is missing. 

 " Si cette opinion est juste, on pourrait en tirer comme conclusion qu'a im certain 

 moment, sur les animaux voisins des Lagomys, il y a une tendance a la simplification du 

 systeme dentaire, d'abord par la fusion de la derniere dent avec ravant-derniere, et 

 ensuite par la tendance a la disparition de cet element sonde " *. Filhol here ignores 

 the circumstance that all the anterior teeth have this "troisieme lobe " as well, wbile in 

 their case we have not at our disposal an occasional small isolated tooth to suggest a 

 fusion theory. Besides, as was said before, this theory may be at once disposed of by a 

 glance at our fig. 7, showing m. 2 with a well-developed terminal cusp {t), m. 3, the 

 supposed homologue of this latter, being liliewise present. Other figures also (figs. 10, 

 16) show m. 2 with the terminal cusp, together with the alveolus of m. 3. 



As will be seen further on, Schlosser seems to incline to the opinion that the presence 

 of a terminal cusp in m. 2 of T. viseiiooiensis is an indication of mTs having become fused 

 to m. 2 ; for he says that m. 3 of Lagopsis verus may be the analogue of the terminal 

 cusp (f) in m. 2 of Tltanomys f. It is, however, difficult to make out what meaning 

 he wishes to attach to this vague term " Aualogon ". 



Lagopsis. — The type-specimen, Hensel's Lagomys venis X,\\ii^ ^xa lower cheek-teeth, 

 the last being a small cylindriform tooth, precisely as in the recent Lagomys, to which 

 Lagopsis is closely related. The tooth in question was not complete in Hensel's 

 specimen, but a fragment seems to have remained inside the alveolus ; else he would 

 have presumably used the term " ausgefallen," whereas he says, sj)eaking of the condition 

 of this tooth, that it is broken away (" weggebrochen "). 



Three more or less complete mandibular rami, from Deggenhausen, Elgg, and Hohen- 

 lioven respectively, are mentioned by 11. v. Meyer, and drawings of their teeth, found 

 among H. v. Meyer's MSS. have been reproduced by Schlosser §. They show an 

 agi'eementin their pT^ with HanseVs Lagomys verus, and Schlosser therefore concludes ||, 

 rightly, I think, that they are of the same species. He further deems it not improbable Tf 

 that Lagomys wningeiisis, H. v. Mey., from ffiningen may be identical with Lagomys 



* Ann. Sc. Geol. x. p. 28 (1S79). 

 t ' Nager des europ. Tertiiirs," p. 32 (1<S84). 

 X Zeitschr. d. deutsch. geol. Ges. 1856, p. 688, pi. svi. 

 figs. 12, 13. 



§ Op. cit. p. 31, pi. viii. figs. 40, 46, 49. 

 ]| Op. cit. pp. 31, 32. 

 IF Op. cit. p. 32. 



SECOND SERIES. — ZOOLOGY, VOL. VII. 



67 



