BOWELL : KADUL^ OF BRITISH HELICIDS. 157 



place near the seashore. On otlier plants in the vicinity none was to 

 be found, though cantiana, virgata, and itala were abundant. But 

 a reference to Part III will show that all these species have radulse 

 sufficiently distinct. 



Helicella gigaxii. — I have not yet examined with sufficient 

 minuteness. Boycott & Standen have given an account of its 

 radula (Journ. Conch., vol. xiv, p. 165). 



Htgromia ruscA is nearer to gramdata than to any other of our 

 species ; it differs from granulata in the following respects : — 



1. All the unci are relatively wider: centrals and adraedians 

 roughly equal in length and breadth; externals markedly oblong. 



2. The lateral curve of the admedian basal plate is much more 

 pronounced. 



3. The apices are blunter. 



4. External ectocones are more nearly equal in length to the 

 corresponding mesocones. The prevailing number is two, but there 

 may be three, or the original two may be subdivided to form four. 

 These external cones, regarded as groups, show less tendency to slant 

 laterally and anteriorly than those of any allied species. 



Sometimes it is quite difficult to see the medial cusp of the 

 external mesocone, owing to the very regular overlapping which 

 occurs here. If this cusp is not observed, it may easily be supposed 

 that the radula belongs to the type found in the commoner Hygromm. 



^;:i0ror^cfz3cDc3:^ 



It is, however, always present, i.e. this mesocone is undoubtedly 

 bifid. This radula is very distinct. The very short external cones 

 are remarkable. A similar type occurs in Helix spirorhis, Lowe, from 

 Madeira. 



The bifid external mesocone is found in pomatia, aspersa, nemoralis, 

 hortensis, arhustorum, ohvoluta, lapicida, caperata, itala, harhara, 

 granulata, and fusca. It also occurs in Vallonia and Acantliinula. 

 In the allied groups Clausilia shows it, and it is present, though less 

 marked, in Cacilioides. Whether it is really present in the 

 Pijramidulce will be discussed under those species. 



Mr. lleynell kindly gave me the remains of an Eulota fruticum. 

 The radula is very similar to that of H. hortensis, so that in the 

 possible event of abnormal specimens of Th. cantiana being mistaken 

 for fruticum, a ready and certain means of diff'erentiation exists in 

 this character of bifid external mesocones. 



AVe have so few described species among the smaller Helices that 

 comparative descriptions are not required. The Valloma or 

 Acanthinula radula can be distinguished at a glance ; rotundata, 

 rupestris, andpi/gnKewii have striking individual peculiarities. 



Tlie Vallonije difi'er from all other Helicids in the marked 

 diminution of size of the centrals compared with the admedians, and 



