18 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



Steenberg has drawn attention to the pecuUar form of the 

 prostate gland in Acanthinula and Vallonia} In these genera it 

 consists of a small number of moderately long tubules, situated 

 at the posterior end of the common duct, just in front of the albumen 

 gland (pi. II, fig. 5). It is, however, characteristic of the Orthurethra 

 that the so-called prostate gland, instead of forming a compact 

 ribbon extending along the whole of the common duct, consists 

 of more distinctly separate tubules, which sometimes attain a 

 considerable length, but tend to be chiefly concentrated towards 

 the posterior end of the common duct, and are, as a rule, entirely 

 confined to that end in the smaller species. Thus, in Cochlicopa 

 luhrica and Lauria cylindracea we find the same type of prostate 

 gland as in Acanthinula and Vallonia. 



In Patulastra halmei, a much larger species than the others, the 

 prostate gland consists of a large number of separate narrow tubules, 

 forming an irregular fringe, which extends along almost the entire 

 length of the common duct (pi. I, fig. 2). It thus resembles more 

 closely the type of prostate gland found in the Enidae. In Pyramidula 

 rupestris, on the other hand, the gland is greatly reduced, and 

 consists of a few extremely small and narrow tubules at the posterior 

 end of the common duct (pi. II, fig. 4). 



It is interesting to notice that although a prostate gland occurs 

 in Acanthinula lamellata it is absent in those examples of A . aculeata 

 that have no male ducts ; ^ while in the similar specimens of Vallonia 

 it is quite vestigial, being so small as to be only visible in stained 

 preparations under the microscope (compare pi. II, figs. 5 and 6). 

 On the other hand, in the British species of Azeca, in which the vas 

 deferens is unusually broad in comparison with the size of the snail, 

 the prostate gland attains relatively enormous dimensions. While, 

 therefore, the function of this gland remains doubtful, it seems 

 not unlikely that it produces a secretion which normally passes 

 down the male ducts. 



The receptacular duct is long in the genera that we are considering, 

 especially in Patulastra halmei and Acanthinula aculeata, and it 

 is unbranched. In this it resembles all the Orthurethra, excepting 

 Cochlicopa and the Palaearctic Enidse. The oviduct and vagina 

 are without other appendages. 



More than fifty years ago Goldfuss said that Vallonia pulchella 

 and V. costata both possessed darts,* and in 1873 Lehmann stated 

 that Vallonia pulchella had a dart-sac, and showed one in his figures 

 of this species.^ He also showed dart-sacs in his figures of Acanthinula 



closely resembles that of the Pupillidse, and I agree with Dr. Pilsbry in thinking 

 that it should be retained in this family (Man. Conch. (2nd ser.), vol. xxv, 

 1919, pp. 68, 69). 



1 Op. cif., p. 14. 



2 Boycott, Proc. Malac. Soc. Lond., vol. xii, 1917, p. 225. 



^ Verhandl. naturh. Verein. preuss. Rheinl. & Westphal., 1856, p. 52. 

 * Op. cit., p. 92, pi. xi, fig. 30. 



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