4 DIPTERA OF NORTH AMERICA. [PART II. 



ping together, shut the opening ; the species of the genera with 

 a large proboscis, especially their females, can altogether engulf 

 small insects within their proboscis, as if they swallowed them, 

 whereas they only suck them out and throw the remainder away. 

 The horny parts of the mouth are short. The stout labrum has 

 on its lateral edge, which is bent downwards, several deep incisions, 

 thus forming strong teeth. The tongue is longer than the labrum, 

 and lies under it without being encased in it. 



The upper side of the thorax is convex, with bristles inserted in 

 rows, between which there are more or less numerous short hairs ; 

 in some genera there is a flat, somewhat concave declivity before 

 the scutellum. Prothorax and mesothorax are very coalescent ; 

 no distinct collare is perceptible, and the humeral callosities are not 

 sharply limited ; of the ordinary transverse suture only the begin- 

 ning is indicated on both sides by a large, more or less triangular 

 impression. Scutellum with two, four, or six strong bristles ; more- 

 over, its surface is sometimes hairy. The elongated prothoracic 

 stigma is closed. Immediately above the basis of 'the fore coxae 

 there is a strong bristle, seldom several. The metathoracic stigma 

 is unusually small. The epirnera of the metathorax have a very 

 large development ; they embrace often the basis of the abdomen 

 from the side to a considerable breadth, and extend as a narrow 

 stripe along the basis of its upper side. 



The abdomen of the female has seven segments, the last two of 

 which are generally very narrow and contracted under the pre- 

 ceding ones, so that only five segments appear on the outside ; the 

 seventh segment, in the female, bears on its end two small lamellae 

 connected with it by an articulation and fringed with hairs ; above 

 them there is, in many species, a fan-shaped row of short, stiff, 

 thorn-like bristles ; in other species the number of these thorns is 

 reduced to four or two ; sometimes they are altogether wanting ; 

 the latter is especially the case with those species which prefer dry 

 localities, or also those, the hind part of the thorax of which has 

 a flat usually concave declivity ; this difference in the structure 

 of the ovipositor has certainly some relation to the difference of 

 the locality where the eggs are deposited ; it is possible that a 

 complete fan of thorn-like bristles constitutes a peculiarity of the 

 species the larva? of which live under ground, whereas it is wanting 

 when the eggs are laid in decayed wood. 



The abdomen of the male can also be considered as consisting 



