104 



PBOCEEDINGS OP THE MALACOLOGICAL SOCIETY. 



that they belong to separate sub-genera, and not improbably 

 to distinct genera. 



When, however, we try to decide which of the many other 

 species from Troj)ical Africa should be most closely associated 

 with either of these forms, great difficulties arise, chiefly owing 

 to our lamentable ignorance of their anatomy. Pollonera ^ and 

 Pilsbry ^ have figured the reproductive organs of H. aloysii- 

 sabaudicB, and they closely resemble those of H. gomesianus ; but 

 an examination of a slightly immature specimen of that species 

 in the British Museum shows that this resemblance does not 

 extend to the other organs ; for in H. aloysii-sahaudicB the cerebral 

 and buccal commissures are extremely short — very different from 

 those shown in PI. Ill, fig. 4 — the lung is longer, and the marginal 

 teeth of the radula are of a quite different type, having short 

 curved bifid cusps, rather like those of H. cryptophalhis although 



Fig. 2. — Representative teeth from the radula of Helicarion aloysii-sahaudicB, 

 Poll., Bumaks Island, Victoria Nyanza." x 200. 



the teeth are not so narrow and crowded, the formula being 

 (31 + 19 -[- 1 + 19 + 31) X 110. H. aloysii-sahaudice therefore 

 appears to belong to a separate group of these snails. According 

 to Thiele,* H. plicatulus, Mts., H. sowerbyanus (Pfr.), and possibly 

 H. masuJcuensis, Smith, also have genital organs like those of 

 H. gomesianus, while the same seems to be true of H. medjensis 

 (Pilsbry),^ but without further knowledge of their anatomy it is 

 impossible to say whether these forms are more nearly related to 

 H. gomesianus or to H. aloysii-sabaudice. Externally, H. plicatulus 

 seems to differ from both these species in having a dark band on 

 each side of the animal's neck ^ and a protoconch without any 

 trace of spiral sculpture, * while H. medjensis and H. masukuensis 

 are also stated to have smooth embryonic whorls. In H. welwitschii 

 (Morelet) the radula approaches that of H. gomesianus more nearly 



^ Spiidizione al Ruwenzori di Prlnc. Luigi Amadeo di Sovoia, vol. i, 1909, 

 pi. iii, fig. 15. 



2 Bull. Amer. Mus. Nat. Hist., vol. xl, 1919, p. 277, fig. 140. 



^ Deutsch. Zentral-Afrika-Exped. (1907-08), vol. iii, 1912, pp. 189-199, 

 pi. vi. 



« Bull. Amer. Mus. Nat. Hist., vol. xl, 1919, pp. 277-278. fig. 142. 



5 Von Martens, Monatsbr. Akad Wissensch. Berlin, vol. xxvii, 1876, 

 pi. i, fig. 5. 



6 D'Ailly, Bihang K.Sv. Vet. -Akad. Handl., vol. xxii, pt. 4, 1896, p. 30. 



