BOWELL : RADUL^ OP BRITISH HELICIBS. 127 



Acanthimila aculeata resembles Vallonia except in the possession of 

 a very much greater number of laterals. The marginals in these 

 (three or more ?) species are regular little combs, and quite similar 

 to those found in the Vertiginidse. Several varieties of Vallonia 

 occurring in this country possess distinct forms of radulse ; they have 

 a great tendency to asymmetric laterals, one or two rows being 

 enlarged at the expense of the others. The laterals of aculeata are 

 exceptionally regular — another instance of character inversion in 

 closely allied species. 



Helicodonta ohvoluta is distinguished by the unusual angularity of 

 the cusps throughout the radula ; they form a pattern very suggestive 

 of holly-leaves. In Selicigona lapicida, on the contrary, every cusp 

 is rounded off, almost squared off ; but the teeth do not appear to be 

 exceptionally strong in build. Yet their general disposition is similar 

 to that seen in Helicodonta ; it might be supposed that (with those of 

 fusca ?) they were the prototypes of the true Helices. 



The radula of arhustorum seems intermediate between these 

 {Helicigona) and those of the true Helices. The tendency is towards 

 the latter, but they are still quite separate from them. 



Of the remaining species, aspersa, pomatia, nemoralis, hortensis, and 

 Pisana, it may be said that they form a very well-defined group, 

 easily separable at once from the others. The marginal mesocone is 

 always pronouncedly blunt and bifid, resembling a little hand with an 

 extra thick thumb, the fingers being apposed. Each of these five 

 species may be distinguished by special points of minor importance, 

 but their general resemblance is great. The South European group, 

 of which splendida is an example, also belongs here. 



According to this evidence, Selicella and Hygromia would be 

 classed together, or regarded as closely allied, excluding barlara as 

 a form archaic or aberrant, and fusca as being plainly near to 

 Helicigona and Helix (s.s.). To the group of minor Helices, 

 distinguished by Arionid radulae, rotundata may perhaps be added. 

 Acanthimda and Vallonia are close together, and closer to the 

 Vertiginids than to any Helicids. Helix (s.s.) remains a well-mai'ked 

 group, and its relationship to Helicigona is certain. Helicigona 

 should include rupestris, and Punctum pygmceum may remain in the 

 Endodontidge. 



These suggestions are made solely on the evidence arising from 

 the radulse, and I should be the last person to neglect the other 

 evidence, derived from shell, maxilla, diverticula of reproductive 

 system, and even from geographical distribution. But I put them 

 forward here in order to show that the comparative study of radulse 

 may be a great help to systematic malacology or conchology. The 

 radula is a comparatively hard and unalterable organ, and its 

 characters are more constant than those of the diverticula above 

 mentioned, the functions and physiology of which (not to mention 

 their embryology) are still for the most part unknown. 



{To he continued.) 



