232 HUGH AVATSON. 



myriads of minute multicuspid teeth. I have therefore no 

 hesitation in saying that Apera is in no way allied to the 

 Janellidae. 



Nor do I know of any other herbivorous family from which 

 Apera is at all likely to have been derived. And the fact 

 that the carnivorous characters are so highly developed in 

 Apera is against the theory that the genus has been directly 

 evolved from any herbivorous form. It seems cei'tain that 

 the ancestors of Apera must have been carnivorous for a 

 very long time ; and it is not likely that these ancestors 

 would all die out without leaving any descendants excepting 

 this single genus. The question is whether we can find any 

 carnivorous genus of slugs or snails resembling Apera in 

 characters which are not likely to have been developed 

 independently through the common acquisition of predaceous 

 habits. 



Collinge has already pointed out how improbable is the 

 theory of P. and F. Sarasin that Apera is closely allied to 

 Atopus.^ This genus and the other members of the 

 Rathouisiidge differ widely from Apera and every other 

 carnivorous form in a number of important characters, such 

 as the wide separation of the male and female openings, the 

 presence of Sim roth's glands, the structure of the foot, the 

 very large mantle, and the structure of the liver ; while they 

 only resemble them in the radula, the absence of a jaw, and a 

 few other points connected with their carnivorous habits. I 

 agree with Simroth in regarding the Rathonisiidas as 

 being more nearly related to the Veronicellidfe than to 

 any monotrematous carnivorous family ; indeed, I have little 

 doubt that, with the exception of the Veronicellidas and 

 the Onchidiidse, no family of the Stylommatophora is 

 less closely related to Apera than the Rathouisiidee. 



Plutonia, a carnivorous slug found in the Azores, is 



perhaps less unlike Apera than is Atopus; but it differs 



from it in the mantle, the latei'ally compressed form of the 



body, the presence of a jaw, the absence of a penial retractor, 



^ For references, see pp. 111-113. 



