FOSSIL AND EECENT LAGOMOEPHA. 475 



noviensis (fig. 25) it is evident as a small vertical pillar, h'ing far below the triturating 

 surface of tlie moderately worn tooth. 



To return to the second stage in Titcowmys Foiitannesi. The inner of the two 

 principal enamel-inflections resembles somewhat in outline its homologue in Lagopsls 

 verus (PI. 37. fig. 26, p. 2). It is seen to be composed of two parts : a posterior, which 

 communicates by a narrowed opening with the internal margin of the tooth, and thence 

 runs straight towards the middle of the tooth, and an anterior circular one; the 

 two communicating with each other by a narrow channel. The terminal cusp [t] is 

 situated much nearer the inner side than in the first stage. I have dealt with this 

 terminal cusp of the lagomorphous Eodentia on a former occasion, and homologized 

 it with Osborn's hypoconulid * ; a view from which I see no reason to depart. In 

 the third stage (fig. 3) this hypoconulid is still apparent ; but the " paraconid " has dis- 

 appeared, and so has the circular part of tlie inner enamel-inflection. The transverse 

 posterior part of the latter is on its way to be shut off' from the inner margin, and to 

 assume the form of a circular enamel islet. " t " is visible on the posterior internal edge 

 of the tooth. In the fourth stage (p. 2 of fig. 7), the circular enamel islet is quite 

 separated from the inner margin, and lias become confluent with the outer enamel- 

 inflection, so that the triturating surface of the tooth presents — if we except a small 

 enamel fold limiting anteriorly the still extant t — only one enamel-inflection, pene- 

 trating from the middle of the outer margin and approaching the inner. In the fifth 

 stage (fig. 4) we find only the latter inflection, t also having disappeared. This tooth in 

 its general outline again approaches the first stage. 



No lower deciduous teeth of Titanomys are at my disposal. Filhol has figured d, 

 and A.-, of T. visenoviensis from Saint-Gerand-le-Puy (AUier) ; from this figure nothing 

 more can be made out than that in d. 2 the anterior part seems to be more produced 

 anteriorly than in p. 2. No description is given of the triturating surface f. 



The anterior lower premolar of T. visenoviensis is distinguished from the same tooth in 

 T. Foi/faiinesi by the persistence of the enamel-inflection of the inner side in the adult 

 (PI. 37. fig. 25) ; in the immature specimen figured by Gervais, and originally described as 

 a separate species, T. frilob/is, the two enamel-folds are confluent in the middle of the 

 triturating surface, thus comj^letely separating an anterior and a posterior lobe J. The 

 terminal cusp (t) present in the specimen figured (PI. 37. fig. 25) must certainly be 

 expected to be visible likewise in younger specimens ; Gervais makes no mention of it in 

 this tooth ; in the profile view oi the tooth, however i^, there are two vertical grooves on 

 the inner side. A small anterior pillar ("paraconid") on the anterior side (1), lielow 

 the triturating surface, lias already been mentioned as present in the British Museum 

 specimen. -'■ 



■* Proc. Zool. Soe. Lnnaon, i8!t3, p. 203. .'.''■ 



t H. Filhol, " Etudes des Mammif. t'oss. de Saint-Gerand-le-Puy, AlHer," Ann. Sc. Geo), x. p. 29, pi. iii. fig. 3 

 (1879). 



+ Zool. et Pal. Fr. p. .51 : " les denx lobes de la prcmiire [molaire] ny sent point encore reunis I'un a I'aurre par 

 \m petit isthme d'ivoire " ; pl. 46, fig. 1 (1S.59). 



§ O^j. cit. pl. 46, fig. 1 c. 



66* 



