BOWELL : EADtJL^ OF BKITISII HELICIDS. 161 



embryo of Arioti horiensis shows very similar externals and admedians. 

 RoUmdata appears to show a bifid external mesocone, but I do not 

 think the structure is homologous Avith that of the larger Helices. 

 It is not constant, specimens occurring with this cone (or rather 

 blade) simple. This radula does not show close affinity with that 

 of any other of our species, but it is much nearer to that of Hygromia 

 hispida than P. rupestris. Several of the apparently allied foreign 

 forms which I have examined have turned out to have radulge of the 

 Hyyromia type. 



The magnification of each of the accompan5nn<r figures may be 

 ascertained from the scale. The two Vallonia are drawn to the same 

 scale ; the Acanthifiulce and P. rupestris may be measured by the 

 scale shown with the figure of A. acxdeata. In every case each 

 division of the scale represents 10 /t (one-hundredth part of a 

 millimetre^ 



