Notes on South African Mollusca. 129 



species is very like that of Dorcasia, while in Strophocheilus rosaceus 

 from Chili it is almost exactly intermediate between the types found 

 in Dorcasia and Trigonephrus, and the jaw in the latter species is 

 striate, as in the South African subfamily. Plate states that in 

 Strophocheilus ovatus and S. proximus the duct from the posterior 

 division of the liver opens into the muscular part of the stomach, 

 while that from the anterior division opens into the thin-walled part 

 in front of the muscular portion." This is also the case in the South 

 African snails, hut in Acavus Randies states that both hepatic ducts 

 open into the thicker-walled portion of the stomach. f Even the 

 shell of Borus shows some resemblance to that of Trigonephrus in its 

 colouring and the character of the lip ; and in the form of the shell 

 the most elongate species of Trigonephrus are not very unlike some 

 of the South American species, such as Strophocheilus (Borus) 

 lutescens. 



As a whole, however, the South African subfamily is probably not 

 quite so primitive as the Strophocheilinae ; though here again we 

 find that the southern genus Trigonephrus retains more primitive 

 characters than Dorcasia, which is found further north. This is 

 shown by the central tooth of the radula (which in Trigonephrus 

 is of a more primitive type than in almost any other member of the 

 Acavidae), by the shape of the kidney, and perhaps most strikingly 

 by the shell ; for in Dorcasia the shell is depressed, with a widely 

 expanded lip, and has quite lost that resemblance to the Bulimiform 

 members of the family which can still be traced in many of the 

 species of Trigonephrus. There is, however, a small section of the 

 latter genus in which the shell has also become depressed, and in 

 which the reproductive organs have in some respects become more 

 highly specialized than in the other southern species. Perhaps this 

 may be due to a small secondary centre of evolution having arisen 

 in the southern part of the area, where the conditions are more 

 favourable than in the arid regions further north, and where the 

 proximity of the coast may have led to some crowding of individuals. 

 And possibly the evolution of Anoylypta in Tasmania might be 

 attributed to a similar cause. 



The climate of the Cape is much more like that of Europe than 

 that of Brazil, and the South African Acavidae differ from the 

 Strophocheilinae in that they have a strong resemblance in their 

 external features to the true Helices of Europe. Indeed Trigo- 

 nephrus globitlus was once regarded as a variety of Helix pomatia,\ 



* Sitz-Ber. Ges. naturf. Freunde, Berlin, 1896, p. 149. 



t Proc. Mai. Soc., 1900, iv. p. 105. 



\ Chemnitz, Conch. Cab., 1786, ix. 2. PI. CXXVIII, f. 1138c. 



