238 HUGH WATSON. 



would suggest, however, that it is quite possible that some of 

 the South American carnivorous genera such as Guestieria, 

 which Kobelt places in the Streptaxidte, may pi-ove to 

 belong to the Rhytididge when their anatomy has been 

 examined. 



Even if this view of the phylogeny of A per a is accepted, 

 I would not advocate the placing of the genus in the Rhy- 

 tididee. The gap which separates Apera from any known 

 member of that family is a very wide one, and the isolation 

 of the genus is by no means over-emphasized by placing it in 

 a family by itself. 



The Phylogeny of Testacella and its Possible Allies. 



Most modern malacologists are agreed that Testacella is 

 allied to Daudebardia, and that these genera have been 

 derived fi'om Hyalinia or some closely related form. Now 

 it must be admitted that the resemblance between Daude- 

 bardia and Hyalinia is very striking. Whether we regard 

 the nervous system or the i-eproductive system or the excre- 

 tory system, the similarity is equally remarkable. Even in 

 the digestive system the diiference is not very great, for 

 Hyalinia is frequently carnivorous, and most of its teeth 

 have become thorn-shaped, while Daudebardia still retains 

 a small jaw, and the odontophoral muscles in this genus do 

 not completely surround the radula-sac. Moi'eover, the evolu- 

 tion of Daudebardia from Hyalinia is to a great extent 

 recapitulated in development, young specimens of Daude- 

 bardia having a shell very like that of Hyalinia, into which 

 the animal can withdraw itself.^ In my opinion the evidence 

 of Daudebardia alone is almost sufficient to prove that the 

 carnivorous snails and slugs are not monophyletic; for I think 

 that we must admit that Daudebardia has been evolved 

 from Hyalinia or some closely allied form, and I do not 



' See Simroth, H., ' Nova Acta Acad. Cses. Leop. -Carol. Germ. Nat. 

 Cur.,' 1891, vol. Ivi, p. 270. 



