THE C'AENIYOEOUS SLUGS 0¥ SOUTH AFKICA. 163 



phanta liochstetteri [Pfr.) one of the teeth in each row 

 may abnormally develop a double cusp ; but I believe that 1 

 am right in saying- that in no carnivorous genus excepting 

 A per a are some of the teeth normally provided with double 

 cusps, for I regard the bicuspid teeth of Pseudosubulina 

 lirifera {Morelet) as something quite different. What is the 

 reason for this remarkable modification of the inner teeth in 

 these two species ? Perhaps it may be found that Apera 

 burnupi and A. sexangula live chiefly on some special kind 

 of food, and have their radula=i specially modified in conse- 

 quence. Or possibly we have here an instance of carnivorous 

 slugs reverting to a partly vegetarian diet, and the lateral 

 teeth are used in eating vegetable and the marginals in 

 eating animal food. The fact that Collinge has found both 

 animal and vegetable remains in the intestine of A. sex- 

 angula is in favour of the latter view. In case this hypo- 

 thesis should prove to be correct, it is interesting to compai-e 

 the type of radula found in these species with that which is 

 characteristic of the Limacidse, Zonitidee, and other 

 omnivorous families. These also have developed thorn-shaped 

 marginal teeth, very similar to those in Apera, and here, too, 

 we find that the lateral and central teeth are shorter and 

 broader with one or two less pointed cusps. Nevertheless, 

 these inner teeth are very different to those of Apera 

 burnupi and A. sexangula, for they are of the ordinary 

 type with broad oblong bases, such as is found in the great 

 majority of herbivorous snails, whereas in the species of 

 Apera the teeth have narrow bases and have obviously been 

 derived from the thorn-shaped type. This difference, how- 

 ever, could be easily explained by supposing that in the 

 Zonitidse, etc., we have a group of herbivorous snails which 

 have become adapted to a partially carnivorous diet, while in 

 these species of Apera we are dealing with carnivorous slugs 

 which have become partially herbivorous. 



Further details about the radula of Apera will be found 

 under the head of the different species. I need only add here 

 that the teeth towards the hind end of the radula are more or 



