315 



Family STRATIOMYIIDAB 



The larvae of this family are readily separated from those of any 

 allied family by their characteristic general appearance (PI. XLVII, 

 Figs, i, 2, 3), and the finely shagreened surface of the body. All 

 the genera so far described have larvae that differ appreciably in the 

 following details : head structure, chaetotaxy, indentation of lateral 

 margins of abdominal segments, length and structure of the apical 

 segment, and structure and armature of the anal respiratory chamber. 

 In the aquatic forms the apical respiratory chamber, which contains 

 the openings of the spiracles, is furnished along its margins with long 

 plumose hairs. When the larva is close to the surface of the water 

 the anal extremity is curved upward till the tips of the respiratory or 

 spiracular chamber are free of the water, the radiating hairs then ex- 

 panding upon the surface film and preventing the water from flooding 

 the chamber and interfering with respiration. When the larva de- 

 scends below the surface the hairs are drawn inward, enclosing a 

 large air-bubble which is carried in this manner until nearly exhausted, 

 when the larva again ascends to the surface. The terrestrial forms 

 lack the plumose hairs bordering the anal respiratory chamber and 

 the latter is in some genera located upon the disc of the segment some 

 distance before the apex instead of at the extreme apex as in the 

 aquatic forms. 



No other species in Orthorrhapha known to me, except a few in 

 Cecidomyiidae, transform\to the pupal stage within the larval skin, 

 and because of this peculiarity it will only be necessary to give a key 

 to the larvae in the family. I have mainly used material in the 

 Laboratory collection in drawing up the keys presented, but in a few 

 cases I have also made use of published descriptions or borrowed ma- 

 terial. 



CHARACTERS OE THE FAMIEY 



Larvae and Puparia. — Twelve-segmented exclusive of the head, 

 the latter attached at middle to first thoracic segment, and usually 

 with a distinct ocular prominence on each side at varying distances 

 from front margin and numerous long hairs on dorsum and venter; 

 antennae distinct ; pseudopods absent, penultimate and antepenultimate 

 segments sometimes armed with locomotor hooks on caudal margin 

 of ventral surface; anterior spiracles near posterior margin of side 

 of first segment; lateral metathoracic and abdominal spiracles present 

 or absent; posterior spiracles separated, located in a transverse slit- 

 like cavity which may be apical or preapical and fringed with long 

 plumose hairs or unfringed; entire surface of body finely shagreened. 



