FOSSIL AND KECENT LAGOMOEPHA. 461 



Schlosser bases his new genus Lagopsis on the differences (froua Layomys) in the shape 

 of the anterior lower premolar (p. 2), " und das, wie es scheint, haufige Fehlen des vierten 

 Molaren," thereby meaning the lower m. 3. I agree with the first proposition; as to the 

 latter, it will be shown later on that in all the specimens of Lagomijs verus, in wliich 

 m. 3 is missing, it has simply dropped out, for its alveolus is present. 



The upper teeth of Lagopsis, which are here described for the first time, although more 

 closely resembling Lagomys than Prolagus, present, however, characters which strengthen 

 the conclusion based on the lower teeth, viz. the establishment of a separate genus. 

 Lagopisis realizes the penultimate stage in the evolution of the cheek-teeth of Lagomyidse, 

 Lagomys the last. 



The description of the upper cheek-teeth of Lagopsis may be appropriately preceded by 

 that of Lagomys *. The numerous existing species of Lagomys show a considerable 

 constancy in the pattern of their cheek-teeth. Young individuals were not available to me. 

 In the adult we find a further step away from the Titanomys type ; not only the two true 

 molars, but the posterior premolar (p. 1) likewise, have lost every trace of the crescentic 

 enamel folds, so that p. 1 has become very similar to the true molars, all three showing 

 the transverse fold proceeding far outward. P. 2 exhibits, in a very interesting manner, 

 a reduction of the Titanomys tyj)e. There is no transverse fold, the original internal notch 

 being maintained ; of the tAvo crescentic enamel folds (/;) and (e) only the former, 

 the internal, remains, and it bears on its outer side a strong cusp (6) and opens on the 

 antero-external margin of the tooth. P. 3 shows a further reduction as compared -with 

 Prolagus. Of the internal notch only a feeble vestige is visible, and of the two typical 

 enamel folds only the internal one, which runs obliquely from the middle of the anterior 

 margin in a postero-external direction. 



Deperet has figm-ed from La Grive a left palate devoid of teeth, but exhibiting very 

 distinctly the alveoli of the five cheek-teeth ; he assigns this fossil, quite rightly in my 

 opinion, to Lagopsis verus f . 



Among the fossils collected by myself at La Grive are tAvo rooted upper cheek-teeth 

 (Brit. Mus., G. D., No. 5264), which in size agree with the lower teeth of Lagopsis 

 verus from the same deposit. Lagopsis being the one Tertiary genus Avhich, by the form 

 of its lower teeth, comes nearest to Lagomys, it covild be anticipated that the upper teeth 

 of the fossil would likewise show a near approach to the recent genus, and this is, 

 in fact, the case. Additional evidence is furnished by a specimen from CEningen, to 

 be described later on. 



One of the isolated teeth just mentioned, from La Grive (PI. 36. fig. 31), exldbits the 

 same somewhat triangular outline — the apex being turned outward — and about the same 

 characteristic enamel folding (6) as the upper p. 2 of Lagomys. In the p. 2 of LMgomys 

 the outer enamel border of the crescent {h) is raised into a strong triangular cusp, with its 

 convexity turned inward ; in the fossil tooth the inner border of the crescent is raised in 

 the same manner. From p. 2 of Prolagus oeningensis (Kon.) (PI. 36. fig. 21) the tooth 



* Enlarged horizontal sections of the u^jper cheek-teeth of Lar/omi/s aJpinni, and L. nejialaisis are given by Heusel, 

 op. cit. pi. xvi. figs. 1 & 5. 



t Ojo. cit. p. 164, pi. siii. fig. 17. 



