464 DE. C. I. rOESTTH MAJOR ON 



In a skull of L. nujricolUs from Ceylon (B. M. Z.D. No. 81.4.29.7) (PL 36. fig. 34) I 

 find that the modernization has l:)egnn to invade p. 3 also ; in the tooth of the right 

 side the internal notch {a) has assumed the shape of a lengthened fold, stretching half- 

 way across the crown and provided with plications as in the other molars. 



M. 3 of Lepns is a small, vanishing cylindrical tooth ; in rare cases, however, of 

 L. eurojjcens a transverse fold has been observed in this *. 



Now as to the condition of the teeth in the young of Lepus. Hilgendorf stated long 

 ago f " that the upper cheek-teetli of young Hares are jirovided with a crescentic enamel 

 tube, which forms a transition to the fossil Ilyolayus." This is perfectly true, but it is 

 not all. 



In the Rabbit Oryctolagus cunicuhis, the two posterior upper deciduous teeth when 

 worn, and the permanent molars when slightly abraded (PL 36. fig. 5), exhibit a pattern 

 identical to that presented by the two anterior true molars of PalcBolagus, as figured in PL 36, 

 fig. 36, viz., an internal notch and a central crescentic enamel fold. Before attrition has 

 set in, they exhibit besides a strong crescentic cusp (6), which delimits the outer side of the 

 enamel fold (fig. 1). On the outer side of the cusp is seen a minute and shallow enamel 

 fold, incompletely dii-ided into an anterior and a posterior part by a ridge descending from 

 the middle of the outer slope of the cusp (c, figs. 1, 5). In d. 2 the anterior horn 

 of the larger crescentic enamel fold stretches further outward than in d. 1, and almost 

 reaches the outer border of the tooth. When attrition is going on, the shalloAver outer 

 fold may be seen for a short while on tlie triturating surface, under the form of one or 

 two minute enamel islets, which are soon completely Avorn away. The deeper inner 

 crescentic fold {b), apparently that mentioned by Hilgendorf, persists longer. 



Here then we still meet with, in an epliemeral condition, the elements constituting the 

 Titanomys-tooih. : two enamel folds {b nnd c) separated by a strong cusj) (6) and an 

 internal notch («). The deciduous teeth of Leims s. 1. are cast olf without presenting 

 any other change except that produced by furtlier wear (fig. 26). In the permanent 

 teeth (PL 36. fig. 17) the internal notch begins to extend. That this growth takes place, 

 in these initial stages at least, wholly in an inward direction — by a prolongation of the 

 two internal cusps, which have gradually been transformed into transverse lobes % — 

 becomes evident when Ave compare these teeth before attrition and in a moderately 

 worn condition. In the former stage the crescentic fold is separated from the internal 



* Hilirendorf, in Monatsber. K. preuss. Akad. der Wiss. Berlin, 14 Dec. Ifi65, \). 073. t Und. 



X " 8 " and " 9 " in the iigures of all the upper cheek-teeth on Pis. 36, 37, 39. The scarcity of my material 

 prevents me from entering into particulars with regard to the young stages of other recent Leporidas, In a slightly 

 abraded p. 2 of Caprolagus hispidus (PL 36. fig. 27), h and c surround almost completely the well-developed 

 cusp (6) and unite together to form a common outlet on the antero-external side of the tooth. The enamel 

 exhibits numerous secondary plications characteristic of the teeth of this Hare. In the deciduous teeth oi Syhilagus 

 brasiKeiisis (PI. 38. fig. 20), a and b are united and present the pattern of a branched fork, visible also in 

 young stages of permanent teeth : in the latter (?<), represented by the two branches of the fork, soon disappears 

 from the triturating surface. In the true Hares, Lepus s. str. (PI. 36. figs. 22, 2-5, 2!S), the primitive pattern is 

 more ephemeral still than in the Eabbit ; the enamel crescent {h) is quite superficial. As is generally the case in 

 disappearing structures, these vanishing elements present a considerable amount of variation in diflFercnt specimens 

 of the same species. 



