THE CARNIVOROUS SLUGS OF SOUTH AFRICA. 157 



(PL XVI, fig. 89). The centre of the cushion is loosely 

 filled with connective tissue. Immediately surrounding the 

 whole radula-sac is a thin layer of circular muscles. 



Around the periphery of the hind wall of the buccal cavity 

 there is a circular groove, which is deepened dorsally and 

 ventrally (PI. XVIII, figs. 115, 116). The dorsal pocket is of 

 no great depth, and is connected with the opening of the 

 radula-sac by a median vertical groove. The ventral pocket, 

 on the other hand, is much deeper, and contains the anterior 

 end of the radula, which is thus folded back below the 

 remaining part in the radula-sac (PI. XVII, fig. 92) . Between 

 the opening of the radula-sac and that of the ventral pocket 

 there is a slight projection formed by the front end of the 

 odontophoral support covered by the radula, and it is this 

 projection that is the first to appear when the odontophore is 

 protruded through the mouth. 



The Radula. — The general appearance of the radula, when 

 freed from the surrounding tissue, is shown in PI. XVII, figs. 

 97, 98, 99, 102, 107, and 114. It is long and relatively narrow, 

 its breadth being sometimes less than one-sixth of its length. 

 The teeth are thorn-shaped with narrow bases, and they are 

 arranged in rows which diverge obliquely forwards on each 

 side of the middle line. In other words, the radula of Apera 

 is of the same general type as is found in the Rhytidida3, 

 the 01eacinida3, the Testacellidae, and, indeed, in 

 all the families of carnivorous snails and slugs excepting 

 the Strep taxi das, in which the teeth are of a slightly 

 diiferent shape. Nevertheless, the radula of Apera is excep- 

 tionally interesting, and shows a diversity which is scarcely 

 surpassed in any genus of the Pulmonata containing so few 

 species. 



In the first place, the size of the radula varies enormously. 

 In Apera gibbonsi and A. parva the radula is extremely 

 large ; when flattened out it measures about a third of the 

 total length of the animal, and in the former species it is pro- 

 portionately broader than in the other members of the genus. 

 In A. dimidia the radula is scarcely a sixth of the length 



