WATSON : AFFINITIES OF PYRAMIDULA, ETC. 21 



(pi. I, fig. 3), or the difierent character of the prostate gland (fig. 2). 

 But the reproductive organs of Patulastra do not agree at all closely 

 with those of any other genera with which I am acquainted, and in 

 its radula (text-fig. ic?), as well as in most other features of its 

 anatomy, it bears a strong resemblance to Vallonia. It would 

 therefore seem best to assign Patulastra to the same family as 

 Vallonia and Acanthinula, although it might perhaps be placed 

 in a separate sub-family, unless any of the other foreign species 

 of Patulastra should prove to have genital organs less unlike those 

 of Vallonia and Acanthinula than are these organs in P. balmei. 



Pyramidula differs from Vallonia and Acanthinula little, if any, 

 more than does Patulastra, for while its radula is of a rather different 

 type (text-fig. 4a), its reproductive organs are not quite so dissimilar 

 (pi. II, fig. 4), and although it differs from Vallonia and Patulastra 

 in the posterior origin of its penial retractor, it agrees in this respect 

 with Acanthinula. The broad mesocones of the central and lateral 

 teeth of Pyramidula rupestris may be due to its habitat (see 

 p. 13), but this would not account for the larger central teeth, 

 which are also possessed by P. humilis (Hutton) . Now, similar central 

 teeth are found in most of the Pupillidae, and, apart from the 

 broadened cusps of P. rupestris, the type of radula occurring in the 

 genus Pyramidula agrees exactly with that usually found in that 

 family. Pyramidula also closely resembles the Pupillidse in its 

 reproductive system, as well as in its central nervous system, pallial 

 organs, retractor muscles, etc. Its black hermaphrodite duct 

 resembles that of Vertigo moulinsiana and V. antivertigo, and the 

 spirally coiled head of the spermatozoon (pi. II, fig. 1) agrees closely 

 with that of Lauria cylindracea ; while its exceedingly short lower 

 tentacles also remind one of the Pupillidse. Indeed, there seem to be 

 no differences between PyramAdula and an ordinary member of the 

 Pupillidse, excepting in the form of the shell and the simplicity of 

 its peristome.^ But these differences in the shell disappear if we 

 compare Pyramidula, not with a full-grown Pupilla, but with a 

 young specimen, for many genera of the Pupillidae have Heliciform 

 umbilicate young, closely resembling the more conical varieties of 

 Pyramidula. I would therefore suggest that Pyramidula is a member 

 of the Pupillidse in which the reproductive organs develop early, 

 and the animal devotes its energies to providing its numerous 

 offspring with well-developed shells before they are born, instead 

 of completing its own shell. 



A parallel case among British snails is found in Balea perversa. 

 This species is also viviparous, and is very like a young Clausilia ; 

 it forms no clausium, and never completes its aperture in the 

 elaborate manner which is characteristic of that genus. Yet, as 



^ Hesse, in a paper just received (Nachr. Deutsch. Malak. GeselL, 1918, 

 p. 110). upholds similar views to mine, but the species he terms Pyr. rupestris 

 seeiiis to differ from that examined by Moquin-Tandon and myself. 



