252 HUGH WATSON. 



Ill my opinion these facts are sufficient to prove that the 

 Oleacinidae have not been evolved from the Rhytididte, 

 but have arisen directly from a gnathophoroiis family. 



Perhaps it might be said that the 01eacinid.Ee cannot 

 have been evolved from the Achatinidae, because in the 

 latter family the central teeth of the radula are almost 

 invariably much smaller than the laterals, whereas iu the more 

 primitive members of the Oleacinidae the central teeth are 

 sometimes nearly as large as those on each side of them, not- 

 withstanding that the teeth in the middle of the radula tend to 

 diminish in size among carnivorous genera (cf. figs. 7, A and b). 

 But I do not maintain that the Oleacinid^ have been 

 evolved from any of the recent genera of the Achatinidae. 

 It must be remembered that already in Upper Cretaceous and 

 Eocene times the Oleacinidge were represented by forms 

 which can hardly be regarded as primitive; the family, 

 therefore, cannot have arisen very much later than the 

 Jurassic period. Now the small central teeth are not an 

 absolutely constant feature of the Achatinidee even at the 

 present day, and it is not improbable that in Mesozoic times 

 the radula was still of the more generalised type found in the 

 closely allied family Megas piridfe. Indeed, it is possible 

 that in the Jurassic period the Achatinidae may not yet 

 have definitely separated from the Megaspiridae. Callio- 

 nepion may perhaps be regarded as a descendant of a 

 form intermediate between these two families, and in this 

 genus the central teeth are nearly as large as the laterals. 

 Moreover, the penis has a continuation in Callionepion, 

 which reminds us of the similar structure found in Eug- 

 landina liebmanni [Pfr.), and other members of the 

 Oleacinidae.^ Lastly, the shells of the typical section of 

 Spiraxis in some respects resemble the Megaspiridae 

 quite as much as the Stenogyrinae, which also suggests 

 that the Oleacinidte may have diverged from the Acha- 



' Pilsbry and Vanatta, ' Proc. Acad. Nat. Sci. Phila.,' 1899, pp. 371- 

 373, pi. XV, figs. 3, 8, and Pilsbry, 'Man. of Conch.,' 1904, vol. xvi, p. 178, 

 pi. xxxi, figs. 7, 8. 



