102 



PROCEEDINGS OF THE MALACOIOGICAL SOCIETY. 



Anadetms, Helper avion, Ariolimax, Hemqjhillia, and Binneya are very 

 near it, each being- barred by some special modification whicb cannot 

 reasonably be attributed to the ancestral forms, such as the extremely 

 narrow foot-margin in Anachnus, the introverted penis in Ariolimax, 

 the unusual insertion of the retractor of the penis in Hemphillia, etc. 



Geomalaous 



Prophysaon 

 Auadeuulus 



Arion 



Letoiu'neuxia 



Auadenus 



Cryptostracon ?- 



Hesperarion — _g 



-Ariolimax Aphallarion 



Hemphillia 



— Binneya 



Eudodoutida3 PliiloraycidaB 



Eegarding the position here ascribed to Philomycus, further observa- 

 tions will be published before long. It need only now be said 

 that the specialization of the muscles has followed much the same 

 course as indicated in Arion, but has proceeded further. Simroth's 

 conclusion that "die Mantelhohle sich mit dem Mantel zusammen 

 colossal erweitert hat, so dass sie diesen in ganzer Lange vom Korper 

 trennt, denn bei eiuer JNTacktschnecke kann unter Mantelhohle wohl 

 nur die Schalentasche verstauden werden," seems to require revision. 

 The lung, or mantle- cavity proper, is not enlarged in Philomycus; 

 but the empty shell-sack, which is si^jyaratecl from the lung-cavity hy 

 an imperforate memhrane, is nearly coextensive with the mantle. 

 The two cavities — that of the shell formed by invagination from 

 the outer surface of the mantle, and that of the lung excavated 

 beneath the mantle — are of totally distinct genesis, and, so far as my 

 observations go, they never coalesce, although in many forms they lie 

 in close proximity. 



