THE CAHNIVOBOUS SLUGS OF SOUTH AFRICA. 121 



dorsal area, palest at the edges, but a little darker in the 

 middle; below them the colour shades off gradually towards 

 the foot. This arrangement of the pigment is best developed 

 in Apera dimidia (PI. VIII, figs. 20 and 21), but it is also 

 fairly conspicuous in A. liurnupi, where the dark mottling 

 is concentrated to form a band on each side below the 

 upper keels. In A. sexangula and A. purcelli the 

 bands, though present, are less noticeable and the colour 

 is more evenly distributed, although the edges of the keels 

 of A. sexangula are almost free from pigment. 



It will be seen that in these four species the pigment tends 

 to form a pattern similar to that found in the genus Arion. 

 On the other hand in Apera giV)bonsi the scheme of colora- 

 tion is different, and the narrow lighter band which this slug 

 usually has along the centre of the back recalls the similar 

 band possessed by many species of Veronicella. It should 

 be noticed that this difference in the position of the greatest 

 concentration of the pigment is not correlated with the 

 difference in the position of the lateral grooves ; for in 

 A. dimidia the grooves are situated as in A. gibbon si, 

 while the dark bands are lower down and occupy a similar 

 position to those of the keeled species. 



Apera dimidia is singular in having small patches of the 

 dark pigment on the foot-sole (PI. VII, fig. 9). But in some 

 specimens of A. sexangula and in at least one example 

 of A. gibbon si minute reddish-brown specks are scattered 

 over the body, and in the former species these extend on to 

 the foot. 



The lighter pigment is usually of some shade of orange, 

 but varies from pale orange-yellow to dull red. It is 

 generally diffused over the whole surface of the body, 

 including the foot-sole, but is often darker above than 

 below, the backs of Apera burnupi and A. gibbonsi 

 rubella being especially deeply coloured. But this pigment 

 is very unstable, and specimens which have been preserved 

 in spirit seldom show more than very slight traces of it. In 

 the case of an example of A. gibbonsi rubella, which was 



