PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



genera the ventral ganglia are much less closely aggregated, the 

 pedal ganglia being some distance from the others, and the abdominal 

 ganglion, instead of having become merged into the right parietal 

 ganglion, is more or less united with the left. Text-fig. 26 shows the 

 arrangement of these ganglia in the three British species of Vallonia, 

 which do not differ appreciably from one another in their nervous 

 system.^ The central nervous system in Pyramidula rupestris and in 

 both species of Acanthinula is almost identical with that in Vallonia. 

 In Patulastra halmei (text-fig. 2a) the visceral loop is somewhat 

 shorter, showing a tendency towards a greater concentration of the 

 ganglia, but the nervous system remains of essentially the same type, 

 that is to say, of a type quite difierent from that found in Helix, 



V. costato, 

 2b 



H. Kisplda 

 2,c 



Pat. baLraei 

 %a 



Figs. 2a-c. — Central nervous system of Patulastra, Vallonia, and Hygromia. 

 The buccal ganglia, commissure, and connectives, which are of the usual 

 type in all these genera, are omitted. (The figure of the nervous system 

 of Vallonia costata might equally well represent that of V. pulchella or 

 V. excentrica.) 



but identical with that occurring in such forms as Lauria cylindracea, 

 Vertigo moulinsiana and V. antivertigo, CocJilicopa luhrica, and 

 Ena ohscura. It is true that a similar arrangement of the ventral 

 group of ganglia also occurs in the Endodontidse, and that the 

 abdominal ganglion of Goniodiscus rotundatus, for example, tends 

 to be united with the right parietal ganglion and not with the left. 

 But we have already seen that the deep peripodial grooves which 

 characterize the Endodontidse do not occur in Pyramidula, Patulastra, 

 Acanthinula, or Vallonia. 



Evidence op the Excretory System. — Perhaps the most striking 

 evidence of the true affinities of these four genera is that afforded 

 by the course of the ureter. 



1 Sterki states (Proc. Acad. Nat. Sci. Phila., 1893, p. 237) that " in V. parvula 

 (and other species) the cervical masses are adjacent to each other in nearly 

 their entire length " ; but this is very far from being the case in, at least, the 

 British members of the genus. 



