THE CARNIVOROL^S SLUGS OF SOUTH AFBICA. 233 



the presence of a secondary ureter, and other characters.^ 

 On the whole it is extremely improbable that Apera is 

 related to Plutonia. It is possible that the latter genus 

 may be allied to the Trigonochlamin^e, but Simroth has 

 given weighty reasons in favour of its having been evolved 

 fi'om the species of the Vitrininfe inhabiting the shoi'es of 

 the Atlantic, and not from any carnivorous group. 



'J'he only other carnivorous forms without external shells 

 which are known to science are the genera from Trans- 

 caucasia placed in the Trigonochl amiuEe. One of these — 

 Selenochl amy s — bears a very striking resemblance to 

 Apera, as will be seen from Simroth's figures.^ Almost the 

 only external differences between Selenochlamy s and 

 Apera are that in the former genus the visible mantle is a 

 little larger, the foot is more distinctly tripartite, and there is a 

 median dorsal keel extending from the mantle to the hind end 

 of the animal. This last difference is the most conspicuous, 

 and yet it is not greater than the difference between Apera 

 sexangula and A. gibbonsi, dimidia, or purcelli. 

 And when we turn to Simroth's description and figures of the 

 internal anatomy of Selenochlamys, we at once notice the 

 similarity between the radial buccal retractors in this genus 

 and those of Apera gibbonsi and A. parva. A closer 

 inspection, however, reveals many differences. The nerve 

 ganglia of Selenochlamys are all separate ; the pedal gland 

 is narrow, straight, and almost entirely embedded in the foot ; 

 the vagina is extremely short ; the right tentacular retractor 

 does not cross the penis. Moreover there appears to be no shell, 

 so that the morphology of the mantle must be quite different 

 to that of Apera. Indeed, I think that there can be little 

 doubt that we have in the superficial resemblance between 

 Apera and Selenochlamys a remarkable instance of con- 

 vergence due to the acquisition of similar carnivorous habits ; 

 and that the only affinities of Selenochlamys are with the 



* Simroth, H., ' Nova Acta Acad. Caes. Leop. -Carol. Germ. Nat. Ciir.,' 

 1891, vol. Ivi, pp. 223-229. 

 2 ' Festschrift Leuckarts,' 1892, pi. vi. 



