THE CARNIVOROUS SLUGS OF SOUTH AFRICA. 119 



development and lower position of the lateral grooves in these- 

 two species is due to the pi-esence of the keels. There ai'e 

 no definite lateral grooves in A. })urcelli. 



The foot-fringe is bounded above by a peripodial' 

 groove, which is usually rather deep (PI. XI, fig. 35). In 

 Apera burnupi and A. sexangula there is a second 

 groove, parallel to the peripodial groove, but sepai'ated from 

 it by a narrow row of rugte, and the radial grooves do not 

 extend below this upper groove, but terminate in it. As a 

 rule the other species have only the single peripodial groove 

 with Avhich the radial grooves unite, but in A. dimidia the 

 upper limits of the lowest row of rugfe are sometimes arranged 

 so as to form an irregular groove parallel to the peripodial 

 groove on each side. 



'J'he foot-fringe itself is narrow and is crossed by a number 

 of small vertical grooves, which are often continued across 

 the edges of the foot-sole. In contracted specimens many of 

 these transverse grooves extend right across the sole, althouo-h 

 they are never so numerous in the middle as at the edges. A 

 conspicuous but irregular longitudinal groove often runs 

 along the centi-e of the foot-sole, but this also is probably due 

 to the contraction of the specimens. In some examples two 

 grooves diverge from a point at the hind end of the foot-sole 

 and extend forward nearh^ parallel to the edges of the foot, 

 thus dividing the hinder part of the sole into median and 

 lateral areas. Occasionally these grooves may be traced 

 forward for about two-thirds of the length of the animal, but 

 they are more usually confined to the hind end, as shown in 

 PI. VII, fig. 9, and in many specimens they are entirely absent. 

 In Natalina I have sometimes found similar grooves towards 

 the hind end of the foot ; but none of the grooves on the 

 foot-sole seem to have so much systematic value as those on 

 the back and sides of the slug, for they may be present or 

 absent in different individuals of the same species. 



Colour. — The skin of Apera is coloured, and the colour is 

 almost entirely due to pigment. It is true that specimens of 

 the more darkly coloured species when preserved in spirit 



