THE CARNIVOROUS SLUGS OF SOUTH AFRICA. 115 



A DESCRIPTION OF THE GENUS APERA. 



EXTERNAL CHARACTERS. 



General Shape. — The slugs cuntaiued in the genus Apera 

 are subcylindrical, tapering gradually towards the head and 

 more abruptly at the hind end, the broadest region being 

 usually behind the middle of the animal. The height is equal 

 to the breadth or sometimes slightly less, while the width of the 

 foot varies from three-fifths to scarcely one-half of the greatest 

 breadth of the body. Most of the species are rather slender, 

 especially A. parva and some forms of A. gibbon si; and it 

 is interesting to notice that the latter do not contract when 

 about to rest, after the usual manner, but merely bend their 

 bodies at various angles, in which state, Mr. Burnup informs 

 me, they much resemble the rhizomes of feims. 



Size. — So few specimens of Apera have been examined that 

 the mean dimensions attained by each species cannot be stated 

 Avith accuracy. It seems probable, however, that the average 

 length of each of the three larger species — A. gibbon si, A. 

 burnupi and A. sexangula — lies between 60 and 65 mm., in 

 the case of specimens preserved in alcohol, although occasional 

 examples may reach a length of nearly 80 mm. On the other 

 hand adult specimens of A. dimidia preserved in spirit are 

 only about 33 mm. long, and A. parva and A. purcelli 

 seem to be still smaller species. 



Tentacles. — As usual in the Stylommatophora, there are 

 two pairs of tentacles, the upper pair being retractile and 

 bearing the eyes.^ The lower tentacles are small, and beneath 

 them there is another pair of short processes of a paler colour, 

 which doubtless correspond to the laljial feelers found in luost 

 of the carnivorous genera. 



Genital Opening. — The common opening of the reproductive 

 organs is on the right side of the head, two or three milli- 

 metres behind the right lower tentacle, and about half that 

 distance from the margin of the foot. 



' See pp. 153, 154 for structural details. 



