WATSON : ANATOMY OF HELICARION. 109 



group of species with separated shell-lobes, to which Pilsbry has 

 applied the name Granularion, since it has yet to be proved that 

 these forms differ from the others in any really important 

 characters, notwithstanding that Pilsbry has placed them in a 

 distinct genus. Unfortunately, H. duporti has never been dissected, 

 and we also know nothing whatever at present about the radula, 

 the nervous system, the cephalic retractors, the pedal gland, the 

 respiratory system, or the excretory organs of any of the species 

 which Pilsbry placed in. either Mesafricarion or Granularion. The 

 forms which he assigns to the genus Gymnarion are probably more 

 nearly related to one another than to any of the preceding species ', 

 yet the only anatomical feature in which the members of this 

 group seem to differ constantly from the other forms is in the 

 character of the male ducts, and they show much diversity among 

 themselves in other respects. 



On theoretical grounds it is not improbable that the resemblance 

 of these African snails to the typical species of Helicarion from the 

 Australian region is largely due to convergence, brought about 

 by the analogous degeneration of the shell and development of 

 the pallial lobes in both regions. But at present there appears 

 to be no justification for assuming that this is actually the case. 

 Helicarion cuvieri, Fer., the type of the genus, seems to be very 

 similar to some of the African forms, not only in its external 

 features, but also in its radula and in its reproductive organs, 

 which bear a single flagellum,^ as in H. auriformis, Thiele. But 

 whether H. cuvieri also agrees with the African species in its other 

 organs awaits further investigation. It would be very interesting 

 to know, for example, whether in the Australian forms the buccal 

 ganglia are bilobed, in the same way as they are, to a greater or 

 less. extent, in all the African Zonitidse that I have examined. ^ 

 For the present, therefore, it would seem best to continue placing 

 all the species from Tropical Africa with a paucispiral shell and 

 a large mucous pore in the genus Helicarion. 



If, however, it is thought advisable, even in our present state 

 of ignorance, to classify in some way the species from Tropical 

 Africa as a basis for further work and criticism, I venture to think 

 that the following tentative classification of the better known 

 species may possibly prove more acceptable than that proposed 

 by Pilsbry. In each group an attempt is made to arrange the 

 species as far as possible in order, beginning with those that are 

 probably the most primitive. 



^ Semper, Reis. im Arch. Philipp., Thl. II, vol. iii, 1870, p. 31, pi. iii, fig. 7 ; 

 pi. vi, fig. 11 ; Thiele, Deutsch. Zentral-Afrika-Exped. (1907-08), vol. iii, 

 1912, p. 190, pi. vi, fig. 57. . 



^ The buccal ganglia do not appear to be bilobed in H. kuekenthali, Kob., 

 from the Island of Halmahera (Wiegmann, Abhandl. Senckenb. naturf. 

 Gesell., vol. xxiv, 1898, pi xxii, fig. 21). 



