364 THE NOTACANTHA. 



whole tribe to which Stratiomys belongs, and is also 

 characteristic of the next group, with this difference, 

 that in the latter the larva-skin contracts after the 

 change into a little oval case, whilst in the present 

 tribe it retains pretty nearly its original form. 



The characters of the insects forming this group are 

 exhibited in full perfection by the species above de- 

 scribed. The proboscis is short, terminated by a 

 fleshy lip, and capable of being withdrawn into the 

 lower surface of the head; its internal parts are of 

 small size, sometimes rudimentary, and the palpi are 

 small and attached to the base of the labium above 

 the bend. In these characters of the mouth these 

 insects approach the following tribe, but the structure 

 of the antennae is always sufficient to distinguish 

 them. These organs, throughout this tribe, are com- 

 posed apparently of three joints, but the third of these 

 distinct pieces always consists of several true joints, 

 as in Stratiomys, and although some of the last 

 of these are occasionally very slender and bristle-like, 

 we never meet with a distinct bristle, such as occurs 

 in most of the flies of the succeeding tribe. The 

 name of NOTACANTHA^, given to this tribe, is derived 

 from an unimportant character, the presence of spines 

 upon the scutellum. This peculiarity, however, does 

 not prevail through the whole tribe, although, as if 

 to make up for the want of it in some species, others, 

 instead of the two spines existing in the typical 

 genus, have a regular comb of six or eight such teeth 

 arranged round the hinder margin of the scutellum. 

 Of this description are the species of the genus Beris, 

 small narrow-bodied flies, usually adorned with me- 

 tallic colours, of which two or three species may be 

 * Gr. notos, the back ; akantha, a spine. 



