456 DR. C. I. FOESYTII MAJOE OX 



Lagomys corsicanvs, Eud. Wagner, op. cit. p. 1139 ; Giebel, Fauna d. Vorwelt, i. p. 99 (1847) ; Gervais, 



Zool. et Pal. franc., first ed. p. 32 (1848), second ed. p. 50 (1859); Lortet, Arch. Mus. Lyon, i. 



p. 53, pi. 8 (1873). 

 Myolagus sardus, Hensel, Zeitschr. deutsch. geol. Ges. viii. p. 695, pi. xvi. figs. 7, 8, 11 (1856) ; Forsytli 



Major, Atti Soc. Ital. Milauo, xv. p. 390 (1873) ; id. Kosmos, vii. (vol. xiii.) pp. 6, 7 (1883). 

 Lagomys (Jlj/o/agus) sardus, Schlosser, Palfeontogr. xxxi. p. 29 (1884). 

 Lagomys sardus, Lydekker, Cat. Foss. Mamm. Brit. Mus. i. p. 256 (188.5), v. p. 325 (1887) ; Schlosser, 



Pal. Oestr.-Ung. viii. p. 86 (1890). 



This Pleistocene species, which is somewhat larger than its Middle Miocene forerunner, 

 closely resembles the latter in its nppcv molars, as the comparison of the figure shows. 

 However, the specialization of the true molars has progressed, for in the teeth of the 

 adult no trace remains of the two crescentic enamel folds (PL 36. fig. 24). P. 1 agrees in 

 the two species. P. 2 is scarcely different in either ; the enamel folds in p. 2 of the adult 

 Trolagus sardus are slightly reduced in size, and the larger inner fold {h) is, in old 

 specimens, sometimes shut out from the outer border by intervening dentine (fig. 24, p. 2). 

 P. 3 has its anterior " wall " somewhat more developed than in Frolar/us ceningensis. 



Of this species I have collected a good number of young specimens. The examination 

 of yoimger stages of the teeth is of considerable interest, as they recall, more than the 

 adult teeth, the primitive features of the TlUmomys-iy^Q. 



Pirstly as to p. 2, This tooth, being the most conservative, shows, as might have 

 been anticipated, the least change from young to old. The diminutive postero-external 

 enamel fold, however, which we met with in a moderately young specimen of P. cenin- 

 gensis, is visible only in very young individuals of Prolagus sardus. 



P. 1, as has been intimated above, exhibits in the young stage a close approach to p. 2 ; 

 the tw^o enamel folds are not yet reduced to the shape of islets, but open freely on the outer 

 side of the tooth (PI. 36. fig. 11) ; the only appreciable difference, apart from its squa,re 

 outline, consisting in this, that the crescentic cusj) (6) wdiich divides the two enamel folds 

 has its anterior horn less produced otttward, so that the folds unite in a common delta 

 on the outer side. The next stage of the still young p. 1 (fig. IG) is the pattern we met 

 with in old p. 2 ; the small external enamel fold (c) alone opens on the outer side, while 

 the larger internal fold has been reduced to the shape of a crescentic islet {b). The 

 third stage is that of the adult, the external fold likewise having become an islet (fig. 24). 



It might be expected that very old specimens of p. 1 Avould show the complete dis- 

 appearance of the islets, as is the case in the true molars ; this condition I have never 

 found in Prolagus sardus, although I have had the opportunity of examining more than 

 a. hundred upper jaws. But it occurs in a Pliocene form of Continental Prance 

 (Koussillon), of which more will l^e said hereafter. 



In the yomigost stages of the anterior true molar (fig). 4, in jaws which still jireserve 

 the deciduous dentition, remains of the two enamel folds are still visible ; they are very 

 imperfectly divided by the last trace of the once powerful intermediate cusp. In a 

 slightly more advanced stage (PL 36. fig. 10 (m. 1), one or two diminutive enamel islets, 

 situated postero-externally to the internal end of the transverse fold, are the last vestiges 



