476 UR- C. I. FOKSYTil MAJOR ON 



We have to follow up this same tooth, ]3r2, ia the other genera of Lagomyidae. In 

 Lagopsis verus (PI. 37. tig- -6), from the Middle Miocene of La Grive-Saint-Alban, the 

 posterior transverse lobe of p. 2 is undivided, with uo trace of t. The next anterior lobe 

 is separated from the former by a T-shaped enamel-intlection on the inner side — which 

 has already been mentioned as approaching in form its homologue in Titanomys 

 Fontcmnesi (tig. 2) — and by an outer one. We have, therefore, here the tAVO enarael- 

 infiections of T. visenoviensis and of the yoimg of T. Fontmmesi. However, in Lagopsis 

 the lobe is more distinctly divided than even in fig. 2 (T. Fontannesi), into an outer 

 and an inner cusp ; for in the former the T-shaped inflection extends more anteriorly, 

 aad the lobe is delimited in front by two smaller enamel-folds. These latter 

 delimit on their anterior side two further cusps, an outer and an inner ; the latter 

 corresponds to 1 (paraconid), as seen by comparison with tig. 2 ; the former may 

 correspond to the pillar ■which in T. visenovienms (fig. 25) is nearer the outer than the 

 i:mer side. In any case, in Lagopsis the anterior part of p. 2 is much more developed 

 than in 'I'ltanumys; for Ave have, in the former, two comparatively stout cusps against 

 one feeble cusp in each of the two species of the latter. Besides, there is in Lagopsis a 

 small odd cuspidule, situated in front of the anterior pair, and in the middle line of the 

 tooth, to which it gives a triangular form. 



The principal difference in Lagomys, to Avhicli Lagopsis is nearly related, consists in 

 the fact that the characteristic T-shajjed inflection of the Lagopsis p. 2 is either 

 absent or replaced by a slight indentation of enamel. The latter is the case, e.g., in 

 Lagomys rutilus *, the former in L. alpinus and L. nepuleiisis f. Moreover, the odd 

 anterior cuspidule has vanished in Lagomys. 



In Prolagus also tlie anterior part of d. 2 is much more complicated than in j^ of 

 Titanomys. Eig. 5, PI. 37, shows this tooth of Frolagtis sardtis, var. cursiiaims, from the 

 ossiferous breccia of Toga, near Bastia (Br. Mus. Geol. Dep. No. M318(5) ; tig. 6, the 

 same tooth of the IVLiocene Frolagiis ccningeasis from La Grive-Saint-Alban ; both from 

 the left side. I liaA'e still younger stages than those figured of tliis deciduous molar, 

 showing the posterior lobe completely separated from the middle one. The anterior 

 lobe of d. 2 of P. ceningensis (fig. 6) is tripartite, as in Lagopsis, but the odd anterior 

 cuspidule is less distinctly divided from the inner than in the latter genus. In 

 tlie tooth of F. a'liingensis the whole tripartite lobe is connected only by cement 

 with the rest of tlie tooth ; in younger stages it is still more divided into a smaller 

 external cusp — which is isolated, also, in the d. 2 of F. sardiis figured (fig. 5) — and a 

 lari;er internal one comprising both the "' paraconid," 1, and the odd anterior cuspidule. 

 The isolated small external cusp of F. sarcitis is situated lar below the triturating 

 surface ; the iimer larger one, showing no sepanited odd cuspidule, is connected on its 

 inner side with the rest of the tooth, as happens likewise, though very rarely, in the 

 corresponding permanent tooth, p. 2, of the same genus. In still more advanced stages 



* For a fi^nu-L'il specimen of this tooth see E. Schiifl", " Ueber Linjonujs rui'dus, f^evertzoft'," i^ep.-Abdr. aus Zool. 

 Jiihrl.i. ii. \>. 09, tig. 5 h. 



t H. Hcustl, " Beitiiige z. Keuiitii. I'ossiler Saiigethiere," Zcitschr. dcutsch. geol. Ges. viii. pi. xxvi. figs. 2 & (i 

 (1856). 



