THE CARNIVOliOUS SLUGS OF SOUTH AFRICA. 117" 



then curving round to meet in a very obtuse angle just 

 above the posterior extremity of the foot. 



The lower keels of Apera sexangula extend on each side 

 along the whole length of the animal, about half-way between 

 the upper keels and the edges of the foot. The slug is thus 

 roughly hexagonal in transverse section, but when it con- 

 tracts the surfaces between the keels become concave. In A . 

 burn up i the lower keels are much nearer the foot than in 

 A. sexangula, and become obsolete towards the hind end of 

 the slug. 



The other species of i^peraare without any traces of either 

 median or lateral keels. They are bluntly pointed at the 

 posterior end. 



There is no caudal mucous pore in Apera. 



Dermal GtROGVes. — In all the species of Apera the back 

 and sides of the animal are covered Avith a network of grooves, 

 dividing the skin into numerous polygonal rugas. These 

 grooves are specially deep in A. burnupi. The centres of 

 the ruga? are often raised in well-preserved specimens, and 

 the skin has therefore a granular appearance. 



Certain of the grooves are larger than the others, and run 

 in more definite directions, forming as it were the main 

 channels from which branch the smaller grooves that form 

 the network. First there are the two dorsal grooves which 

 run along the middle of the back from the respiratory 

 opening to the head. These are most strongly developed in 

 Apera burnupi, and least conspicuous in A. dimidia, in 

 which species the main grooves are scarcely more distinct 

 than the other grooves of the network. The distance sepa- 

 rating the dorsal grooves varies from about one-seventh of 

 the breadth of the body in A. dimidia to less than half 

 that proportion in some forms of A. gibbon si (PI. VII, 

 fig. 4). In A. burnupi, A. sexangula, and A. pur- 

 celli these grooves are separate throughout their entire 

 length, but in A. gibbonsi, A. parva, and A. dimidia 

 they are united posteriorly, and arise from the respiratory 

 opening as a single groove which divides between 3 and 



