THE CARNIVOROUS SLUGS OF SOUTH AFRICA. 251 



are sometimes predaceous/ and that tlieir teeth are liable to 

 alter in form and acquire carnivorous characters. This is well 

 shown in text-fig. 7, A, which represents part of the radula of 

 an African member of the S tenogyri nse ; and Crosse and 

 Fischer - have figured the radula of an American species — 

 Leptinaria lamellata {Pot. & 3Iich.)— in which the outer 

 lateral teeth have become similarly lengthened. Moreover, 

 we find that the radu^la of the more primitive genera of the 

 Oleacinidfe is not of the specialised caimivorous type found 

 in the higher members of the family and in the Rhytididae. 

 Thus in Varicella the radula is usually quite small, the rows 

 of teeth are nearly straight, the bases of the teeth are broader 

 and shorter than in the usual carnivorous type, and there is 

 a small additional cusp outside the main cusp (text-fig. 7, b). 

 This last character is especially significant, as the small cusp 

 is obviously a vestigial ectocone, such as we find in so 

 many herbivorous genera. I am indebted to the Rev. Prof. 

 Gwatkin for kindly allowing me to examine the mounted 

 radulfe of a large number of carnivorous forms, and I find 

 that this additional cusp occurs in all the species of 

 Varicella represented in his collection, namely, V. nemo- 

 rensis Ads., phillipsi Ads., dissimilis Pilshry (= simi- 

 lis Ads.,) and venusta Ads., although it is extremely 

 minute in the last species. It is therefore very surprising 

 that it has been entirely overlooked by previous observers, 

 who have figured the radulse of V. phillipsi and V. 

 nemorensis. Unfortunately I have not had an opportunity 

 of studying the radula of Spiraxis, a genus which may be 

 even more primitive than Varicella; but I have examined 

 that of Pseudosubulina lirifera (ilfore^e^), and find that 

 in this form the second cusp is also present and is larger than 

 in Varicella, although in other ways the radula has become 

 more highly specialised. Strebel has shown, however, that in 

 Pseudosubulina there is a vestigial jaw, the structure of 

 which is not unlike that of the jaw in the Achatinidse. 



' Johnson, C. W., ' Nautilus,' 1900, vol. xiii, p. 117. 

 ^ ' Mission scientifique an Mexiqiie,' pt. 7, 1877, pi. xxviii, figs. 8-10. 

 VOL. 3, PART 2. 18 



