16 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



of Acanthinula have recently been published by Boycott ' and 

 Steenberg,^ and the latter author has also dealt with the genital 

 system of Vallonia costata ; ^ while the details of the reproductive 

 organs of Patulastra halmei, Pyramidula rupestris, and Vallonia 

 pulchella will be seen from Plate I, figs. 2-4 and Plate II, figs. 

 1, 2, 4c, 6. For the purpose of the present paper it will be enough 

 to draw attention here to some of the more striking features of 

 these organs. 



In the first place we notice that in Acanthinula aculeata and 

 Vallonia costata the penis has a long lateral appendix, swollen 

 distally and also near its origin, where it receives one of the branches 

 of the forked penial retractor. Now, a similar penial appendix 

 occurs in most of the Orthurethra, namely in the Enidae,^ Amastridse, 

 and Achatinellidse, in Cochlicopa, and in many of the Pupillidse ; 

 and in the Enidae,^ Pupillidse, and Achatinellidee (excluding the 

 Tornatellininse), the penial retractor is also forked, and sends a 

 branch to the enlarged basal portion of the appendix. On the other 

 hand, a lateral penial appendix of this character is rarely found 

 among any of the sigmurethrous families, although it seems to 

 occur in the Sagdinse,*^ a group of rather doubtful affinities. 



A single specimen of Vallonia costata collected in November, 

 1919, at Little Shelford, Cambridgeshire, possessed a second appendix 

 practically as long as the other, but without the basal enlargement, 

 and arising from the anterior end of the penis (pi. II, fig. 5). Close 

 to its terminal swelling this appendix was attached to the retractor 

 of the right lower tentacle by a very slender muscle, and at about the 

 same place it seemed to receive a small nerve from the right parietal 

 ganglion. A second penial appendix, occupying a similar position, 

 has also been found in a specimen of Ena detrita.'' 



In Pyramidula rupestris the penial appendix is much reduced, 

 being represented by a mere knob (without muscular attachment), 

 which occupies about the same position on the narrow penis as the 

 appendix does in Vallonia costata (pi. II, fig. 4). It is easy to account 

 for the reduction of the appendix in this species. Pyramidula 

 rupestris is viviparous like so many of the Orthurethra, and the 

 embryos before birth attain a relatively enormous size compared 

 with the narrowness of the body-whorl of the parent : they do 



1 Journ. of Conch., vol. xv, 1917, p. 175 ; Proc. Malac. Soc. Lond., vol. xii, 

 1917, p. 221. 



* Op. cit., pp. 2. 6. ' Ibid., p. 9. 



^ Excepting in Chondrula tridcnti (see Moquin-Tandon, Hist. Nat. Moll. 

 France, vol. ii, 1856, p. 298, pi. xxi. fig. 27 ; and Lehmann, Die lebenden 

 Schnechen u. MuscJieln der tjmgegend Stettins u. in Pommern, 181 S, -p. 137, 

 pi. xiii, fig. 46). 



^ Excepting in Ena ■ (Zebrina) detrita. (See Beck, Jenaische ' Zeitschr. 

 Naturw., vol. xlviii, 1912, pi. ix, fig. 25a.) 



^ Pilsbry, 3Ian. Conch. (2ndser.), vol. ix, 1894, pp. 59, 65, pi. xxi, figs. 9, 

 10 ; pi. XXXV, figs. 2, 3, 12. 



' Beck, op. cit., vol. xlviii, 1912, p. 230, text-fig. 23. 



