Notes on South African Mollusca. 127 



organized members of the Acavidae. As in the Caryodinae, the 

 most primitive forms are found in the south of the region, that is to 

 say among the Madagascan species. Some of these have Bulimiform 

 shells, while in the genus Ampelita the egg is only moderately large ; 

 but in all the genera of this subfamily, excepting Ampelita, the 

 embryo attains a relatively enormous size before it is hatched or 

 born (for Stylodonta is viviparous), and most of the Madagascan 

 species, and all those from Ceylon and the Seychelles, have Helici- 

 form or depressed shells. It is true that in some of the species of 

 Acavus the spire is rather high, but this is almost certainly a case of 

 reversion due to their having acquired arboreal habits. There is 

 always a tendency among snails that live on trees or cliffs to become 

 elongated, and the broad aperture of the shell in Acavus suggests 

 that it was originally depressed. Moreover, in the two species of 

 Acavus that are not arboreal, the spire is nearly flat. The shell is often 

 highly coloured, and the lip, unlike that in the Caryodinae, is usiially 

 broadly expanded. Excepting in Stylodonta, all the teeth of the 

 radula are without secondary cusps, and the jaw is without striae. 

 An ureter is present. The reproductive system differs from that of 

 the Caryodinae in being without an appendiculum ; but in the 

 Malagassy genus Ampelita Pilsbry has found that the vas 

 deferens is still closely bound to the penis, as in Anoylypta. 



This subfamily may be named the Acavinae, although Pilsbry 

 originally included under this title the Australian genera also." For 

 our knowledge of the anatomy of this group we are indebted to the 

 researches of Semper,} ViguierJ Sarasin, Pilsbry, |) Wiegmann.lT 

 Bandies, ** and others ; but we still know very little about most of 

 the forms living in Madagascar. 



As the land on which this subfamily arose extended as far as 

 Southern India, one might perhaps have expected to find some 

 members of the group in the peninsula. Possibly they may have 

 once existed there ; but, if so, they were probably unable to survive 

 the competition of the more highly organized snails, belonging to 

 the Helicidae, Zonitidae, and other families, which abound on the 



* Man. Conch., 1895, ix. p. xxxii. 



f Reis. im Archip. Philippin., 1873, iii. pp. 93-100. PL XII, f. 7-10, PI. XVI, 

 f. 5 ; and Nachrichtsbl. d. D. Mai. Ges , 1880, p. 60. 



J Arch. Zool. Exper., 1880, viii. pp. 529-536. PI. XL. 



Ergeb. Naturwissensch. Forsch. auf Ceylon, 1888, i. pp. 35-69. Pis. VI-VIII. 



|| Man. Conch., 1894, ix. pp. 149-156. PL XL VIII, f. 9, 12-14, PL XLIX, 

 f. 19-23, 25, PL LI a, f. 1-6. 



IT Mitteil. Zoolog. Samml., Berlin, 1898, i. pp. 77-81. PL III, f. 3. 



'* Proc. Mai. Soc., 1900, iv. pp. 103-113. PL IX. 



