126 PROCEEDINGS OF THE MALACOIOGICAL SOCIETY. 



is the presence of a deposit of chitin which more or less completely fuses 

 the central cusp with the * endocone ' in the adult radula ; the earlier 

 condition, in which these two were markedly separate, may be seen in 

 the embryo, and in the skeleton teeth at the growing end. Relatively 

 to the basal plates, the teeth are always turned inwards, except in 

 the case of the central tooth. Hence there is always a tendency for 

 the endoconic fold to become hidden and obliterated, and for the 

 ectoconic one to assume greater importance. This latter factor is 

 especially noticeable in small species ; in the larger ones the tongue 

 tends to become wide and flattened, and consequently the distinction 

 between the central and lateral teeth is less and less marked. A 

 mechanical reason for this may be found in the fact that the actual 

 size of the teeth does not vary uniformly with the actual size of the 

 animal. 



The radula of Punetum pygmceum is totally unlike those of the true 

 Helicids ; but it is evidently \evj near to the type prevailing in the 

 Succineidae. The laterals and marginals are multicuspid, the two 

 larger cusps representing the mesocone. The teeth are long and 

 pointed. Carychium minimum presents a very similar state of things, 

 but is much closer to the type prevailing in the Succineidse. It may 

 be worth mentioning that Carychium has a maxilla composed of 

 separate plates, very much like that of a small Planorbis. The radula 

 of Vertigo Mouli?isiana is of the same type as that of Pundum. 



Pyramidula rupestris is an almost exact copy, on a very small scale, 

 of Chilotrema lapicida. It has not the slightest resemblance to 

 P. rotundata. This latter species has a radula very easily distinguished 

 from those of other Helicids, and apparently it is an earlier form ; for 

 it unites some features (tendency to multicuspid marginals, especially 

 in young examples) which remind us of the Pupidae, with a general 

 facies like that of the group next to be considered. I am here 

 speaking entirely of the radula, neglecting for the occasion our other 

 sources of information bearing upon phylogeny. In the sequel I hope 

 to make some suggestions as to their relative importance. 



The next group, judging by the radula, is a large one. It will 

 include virgata, Itala, caperata, cantiana, granulata, hispida, sericea, 

 revelata, and rufescens. These are all very much alike ; the differences 

 which divide them are not greater than those which divide the group 

 of large species of Vitrea which have lately been so much under 

 consideration. All of them show a strong resemblance to the Arionidae, 

 especially to A. hortensis. Here the mesocone in the marginals is 

 represented by a single point, shaped like the blade of a pocket-knife. 

 In other particulars they show an approximation to the true Helices — 

 if such a phrase may be allowed. 



Cochlicella barhara presents a radula as anomalous as the rest of its 

 structure. It even possesses slightly bifid marginal mesocones ; while 

 there is also present a tendency to pectinate form in the extreme 

 marginals that suggests relationship with the Pupidae. 



Hygromia fusca appears to be out of place. Its radula is very 

 distinctive, but evidently has affinities with those of lapicida, 

 arbustorum, rupestris, and (more distantly) of obvoluta. 



