472 DE. C. I. POKSYTH MA.JOE ON 



previously described in this paper. While in all the upper grinding-teeth of Titanomys 

 the initial condition, two crescent folds and an internal notch, is retained throughout life, 

 and this is more or less so in the premolars of ProloQus, in the molars of the latter the 

 crescentic folds are worn away and the internal notch is enlarged to a transverse fold, s 

 in the molars and p. 1 of Lagopsis and Lagomys, and in the molars and posterior premolars 

 of Lepiis s. 1. Milk-teeth and very young permanent molars of Lepus show, with slight 

 variations, the pattern before described as characteristic of moderately-worn teeth of 

 Fulceolagns. No modernization takes place in the latter ; the only change we perceive, 

 by the further progress of wear, is the complete obliteration of the crescentic folds and 

 of the notch on the inner side. In Lepiis, the large crescentic fold of the deciduous 

 teeth, and a small islet external to it — present in some of the species, and representing 

 the external crescentic fold of Lagomyida3 — ^disappear at a very early stage of the two 

 posterior premolars and of the two anterior true molars, and are replaced in the 

 permanent teeth by the transverse fold already described. 



The permanent teeth of Palceolagus, therefore, can only be compared with the 

 deciduous teeth of Leinis; like these (PI. 36. fig. 26), they exhaust their primitive 

 pattern, without evolving a secondary one *. 



Pcdceolagus cannot find a place in our phylogenetic series {Titanomys — Frolagus — 

 Lagopsis — Lagomys). With regard to the condition of their upper cheek-teeth, the 

 species of Palceolagus in which these teeth are known would follow after Titanomys. 

 But they are certainly not the forerunners of Frolagits, except in the form of the true 

 molars ; while Frolagus is more conservative tlian Palceolagtis in the conformation of 

 its two posterior premolars. On the other hand, Falceolagus is certainly the forerunner 

 of Lepns, and presumably its ancestor ; and this cannot be said of the LagomyidcB, in all 

 of which the upper m. 3 has been lost. 



To resume. — We have in the preceding pages followed the transformation in the 

 pattern of the upper check-teeth on three lines : — (1) From genus to genus ; (2) from 

 behind forward in the dental series ; (3) from young to old. 



(1). From genus to genus, we might almost say from species to species, the series is as 

 follows: — Felycocloidty-pe {Felycodus, Flesiudapis) — Titanomys visenoviensis — 1'. Fontan- 

 ^lesi — Falfeolagus — Frolagus ceningensis — F. sardus — Lagopsis — Lagomys — Lepus. 



Felycodus and Flesiadapis are genera of the Lower Eocene. 



Titanomys appears in the Lower Miocene, and vanishes in the Middle Miocene. 



Frolagus appears in the Middle Miocene and lingers on, protected by an insular habitat, 

 until the Neolithic period. 



Lagopsis is at present kno^Ti only from the Middle Miocene. 



Lagomys makes its appearance in the Pleistocene and survives to the present day. 



Lepus, preceded by the Oligocene and Miocene Falceolagus, appears with many of its 

 present generic characters in the Lower Pliocene, and survives to the present day. 



* The remarkable Hare from Sumatra, Nesohgus Netsfluri, approaches Pdlaolagiis more than other recent 

 LeporicUe, inasmuch as, by the feeble development of the transverse enamel-fold (PI. 37. fig. 17), it represents a first 

 stage in the evolution of the secondary pattern. The same form exhibits other primitive features, to be described 

 later on. 



