FOSSIL AND EECENT LAGOMOEPHA, 479 



These teeth, as a whole, exliibit in younger stages a greater longitudinal diameter than 

 in the adult ; this is notably the case in Titanomijs (PL 37. figs. 7, 10, 24), and is chiefly 

 due to the greater develojiment and indepeudence of the terminal cusp {t). 



The youngest mandible of Titanomijs which I possess is a left ramiis of T. Fonfannesi 

 (Br. Mus. Geol. Dep. M5267 h), figured PI. 37- fig. 10. P. 2 and m. 3 have dropped 

 out. Flanking the three corners of the alveolus for p. 2 are visible the small 

 alveoli for the roots of deciduous teeth ; the anterior and the postero-external seem to 

 belong to d. 2 ; the postero-internal was presumably occupied by the anterior root of 

 d. 1. P. 1 is still in the socket and had not yet come into use. Both the principal 

 lobes composing this tooth are surrounded by enamel ; but the wrinkled central surfaces 

 of the lobes are composed of dentine, with the exception, perhaps, of the summits of some 

 of the wrinkles, which, to judge from their shining appearance, mav bear a very slight 

 coating of enamel *. In p. 1 and the true molars of adiiU Tltanomys Fontannesi, the 

 enamel bordering appears interrupted in the middle of the anterior margin (PI. 39. 

 fig. 6 a). Hilgendorf has recorded a similar instance of the absence of the enamel 

 bordering on the inner half of the anterior border in the lower cheek-teeth, p. 2 

 excepted, of Lejy/isf. The anterior transverse lobe of p. 1 (fig. 10) still shows 

 traces of having been divided originally into an outer and an inner cusp and of the 

 " paraconid " on its anterior border ; vestiges of the latter are visible also on p. 1 of a 

 slightly older individual (fig. 16, of the right side), and on m. 2 of the same right ramus. 

 The terminal cusp f (" hypoconulid ") is present in both p. 1 and m. 1 of the younger 

 sj)eciraen (fig. 10), as wxdl as in p. 1, m. 1, and m. 2 of the second individual (fig. 16), 

 and in p. 1 of a third (fig. 21, right side). In the left ramus, exhibiting the complete 

 series of five cheek-teeth (fig. 7), i is present in all of them. In p. 1 of T. visenoviensis 

 (fig. 25) it is remarkably large, although partly fused with the posterior lobe ; and it 

 is equally present on the posterior border of m. 1 and m. 2 of the second specimen of 

 T. visenociensis (fig. 24) ; so that, contrary to what has been stated by former Avriters, the 

 cuspidule in question may be present in all the four anterior cheek-teeth of this sijecies. 



Passing on to the recent representatives of the family, it may be seen from fio-. 22 

 (Pl. 37-), of an immature Caprolaijuti ///.•ijjichts, that p. 1 nearly apjH'oaches p. 2 in its 

 anterior complication. The two principal lobes are not yet connected on the inner side 

 by a dentinal isthmus, but are merely held together by cement ; the anterior lobe is 

 distinctly composed of an outer and an inner cusp, the latter being more pointed and 

 slightly higher than the former. The anterior border of the tooth presents two minor 

 cusps, an outer and an inner, the median odd cusp of p. 2 being absent. Both the lobes 

 show a very marked wrinkling of their surface. As in p. 2, t is apparent on the 

 posterior margin of the second lobe. 



Two very distinct minor cusps are likewise visible on the anterior border of ]). 1 of the 



* We have here an instaucc similar to that recorded by Heusel ia JIus decumaiius, 7-attus, museuhts, si/Juaticus 

 agrarius, and minutus, where in perfectly unworn molars " iiberzieht der Schmelz die Ilociier der Zahnkrone nieraals 

 vollstiindig, sondern liisst an den Spitzen das Zahnbein frei hervortreten." Zeitschr. d. deutsoh. geol. Ges. viii 

 pp. 283, 2S4, pl. siii. figs. 2, 3 (1S56).) 



t Sitzungsber. Ges. naturf. Freunde zu Berlin, 1-i Jan. ISS-t, p. 23. 



