208 PEESH-WATBR AQUABIA. 



of them are so common — except, perhaps, D. punctulatus, wMch 

 may be distinguislied by its somewhat smaller size, and by 

 the perfect blackness beneath its body. 



We have only two species belonging to the genus Acilius : 

 of these A. sulcatus (Pig. 133) is by far the commoner. This 

 beetle is a favourite with aquarium-keepers, and is abundant 

 in still water almost everywhere. It and many of its relatives, 

 near and distant, certainly do not altogether deserve the bad 

 character which some people give them. It is not at all likely 

 that the Acilius sulcatus and other beetles nearly related to 

 him will do any harm in the ordinary aquarium if they are 

 properly and regularly fed. I have kept for many months 

 several beetles of this species in a small tank with a few 



Fig. 133. Acilius sulcatus (Male and Female). 



little fish, and not one fish, to my knowledge, has been hurt 

 in any way by them. These beetles, of course, had plenty of 

 food. Acilius sulcatus is a handsome beetle, and well adapted 

 by nature for an aquatic life. It is a flatter and smaller 

 insect than jD. marginalis : it is Jin. in length, ovate in shape, 

 and greyish-brown in colour. The under-part of the body is 

 black, with the exception that the sides of the abdomen are 

 distinctly and regularly spotted with yellow. The margins 

 of the thorax, and a transverse band in the middle, are a 

 brownish-yellow. In the male insect the first three joints of 

 the anterior tarsi are dilated, and the elyti-a of the female 

 have furrows filled with hairs, these furrows extending to 

 the apex of the elytra. This beetle, when placed upon its back 

 while out of the water, makes a curious noise as it springs to 

 its feet. It also, when out of its natural element, emits, as 



