FOSSIL AND EECENT I-AGOMOEPHA. 463 



a mere vestige of some such element in the same place, the tooth beinj^ presumably 

 more worn than that in the CEuingen specimen. As in the La Gvive tooth, that from 

 ffiningen has both enamel margins of crescent {b) raised into triangular cusps, with 

 the convexity turned inward. 



The anterior premolar, p. 3, of the CEningen fossil is not dissimilar to the same tooth 

 of Prolagus amingensis (Kon.). Whereas in recent Lugomijs the triturating surface of 

 p. 3 exhibits only one enamel fold — starting from about the middle of the anterior 

 margin and running backward obliquely, i. e. postero-externally — the same tooth in 

 Lagopsis shows two enamel folds, as in l?rolagus (eningensis, opening on the anterior 

 margin, and thence running almost straight backward. 



These differences from. Lagomys strengthen, therefore, Schlosser's opinion, that the 

 Miocene fossil is to be considered as a genus [Lagopsis) distinct from Lagomys. At the 

 same time they present a further link in the gradual transformation of the tooth-pattern 

 {Tltanomys — Prolagus — Lagopjsis — Lagomys — Lepiis), which begins in the hindmost 

 molar of Lagomyidae and, gradually proceeding forward, stops at p. 1 in Lagopsis and 

 Lagomys, and at p. 2 in Lcpxis. 



Genus Lepus s. 1. 



It would seem more rational to treat of the Miocene Fal<Bolagiis before Lepus, since 

 there are strong reasons for the assumption that the former is the ancestor of the latter. 

 On practical grounds, however, I tliink it more advisable to give the description of 

 Lepus first, because we can fully understand tlie dentition of Palceolagus only after 

 having dealt with the dentition of the young of the existing genus ; and because, ou the 

 other hand, the latter exhibits a further development of the modernization initiated by 

 Titanomys. 



Hensel, writing in 1856, stated that, contrary to the usual descriptions of authors, the 

 upper molars of Lepus consist each of a single cylinder, which in the second, third, and 

 fourth teeth is provided with a deeji enamel fold, filled with cement and penetrating 

 from the inner side*. When contending that all the previous writers on the subject 

 had incorrectly interpreted the conformation of the leporine molar, Hensel could 

 hardly have guessed that 43 years later he might have made an almost similar 

 complaint. We continually meet with descriptions and figures of lagomorphous animals 

 in which the upper molars are represented as formed by two cylinders closely united or 

 soldered together, presenting three transverse enamel ridges ! 



As compared with the Lagomyidtu, by the presence of m. 3 in the maxillary, Lepus 

 exhibits a more primitive condition. In the characters under consideration, however, 

 Lepus is undoubtedly the extreme member of the series. While in Lagomys the j)Osterior 

 premolar (p. 1) has alone acquired the transverse fold of the true molars, in Lepus 

 (PI. 36. fig. 33) p. 2 has been transformed as well. P. 3 alone retains what we may fairly 

 consider to be the ancestral enamel folds, as well as the ancestral internal notch. There 

 is no anterior " wall " ; wherefore the enamel folds open freely on the anterior side. 



* Zeitschr. deutsch. geol. Ges. p. GSl (IboO). 



