WAiSON : ANATOMY OF HELICARION. 103 



Spermatozoa having spirally twisted heads, about "006 mm. long 

 by less than '002 mm. broad, apparently slightly flattened laterally, 

 and tapering to a sharp point in front. Tail very long and slender, 

 sometimes attaining a length of no less that "3 mm., or fifty times 

 the length of the head. Proximal portion of tail (or " middle- 

 piece ") and head both having the appearance of being furnished 

 with very fine spiral striae. A more conspicuous spiral flange also 

 surrounds the proximal portion of the tail ; it is rather broad close 

 to the head, but gradually becomes narrower posteriorly, until 

 it disappears. 



Affinities. 



Among the many members of the Zonitidae that are found in 

 Africa a large number have been named which bear a close general 

 resemblance to the two species just described. But while these 

 forms all have thin paucispiral shells, well-developed pallial 

 lobes, and a long narrow foot ending in a very conspicuous mucous 

 pore, they seem to show much diversity in their more essential 

 characters. 



The species found in Natal and the Cape of Good Hope ^ 

 resemble H. cryptopJiallus in having an epiphallus bearing two 

 flagella, and also in their type of radula ; but they appear to differ 

 from that species, as. well as from H. gomesianus, in that the 

 cerebral commissure is usually much shorter, the lung is far longer 

 and less richly vascular, the left body-lobe is divided into two 

 portions, and the caudal mucous pore is overhung by a pointed 

 process often of considerable length ; moreover, the detailed 

 structure of the epiphallus, etc., seems to be very difierent. There 

 can be little doubt, therefore, that these South African species 

 are rightly placed in a separate genus from the tropical forms, 

 although it is difiicult to understand why they should have been 

 placed by some authorities in as many as four or five difierent 

 genera, in view of the general similarity of the internal organs 

 of those that have been dissected. 



The species occurring in tropical Africa seem to show a much 

 greater diversity, although very little has hitherto been published 

 about their anatomy. The two forms described in this paper 

 resemble each other closely in their respiratory and nervous 

 systems, but they differ widely in their radulse and in almost every 

 feature of their genital organs ; while they also show less 

 important differences in the jaw, the retractor muscles, the 

 primary ureter, the spermatozoa, the form of the shell-lobes, the 

 coloration of the animal, etc. It can therefore scarcely be doubted 



1 See Pilsbry, Proc. Acad, Nat. Sci. Philad., 1889. p. 279, pi. ix ; and 

 Godwin-Austen, Ann. & Mag. Nat. Hist., ser. viii, vol. i, 1908, pp. 131-133, 

 pi. viii ; vol. ix, 1912, pp. 122-139, 569-585, pis. i-vii, xii-xvii ; vol. xiii, 

 1914, pp. 449-472, pis. xix, xx. 



