STRATIOMVIDAE LEPTIDAE 479 



2')r(scnt. This is a large ianiily, whose members are very 

 diversified, consequently definition of the whole is difficult. The 

 species of the typical sub-family Stratiomyinae generally have the 

 margins of the body prettily marked with green or yellow, and 

 the scutellum spined. In the remarkable American genus, 

 Hermctia, the abdomen is much constricted at the base, and the 

 scutellum is not spined ; in the division Sarginae the body is 

 frequently of brilliant metallic colours. The species all have 

 an only imperfect proboscis, and are not blood-suckers. The 

 larvae are also of diverse habits ; many of those of the Stratio- 

 myinae are aquatic, and are noted for their capacity of living in 

 salt, alkaline, or even very hot water. Mr. J. C. Hamon found 

 some of these larvae in a hot spring in Wyoming, where he could 

 not keep his hand immersed, and he estimated the temperature 

 at only 20° or 30° Fahr. below the boiling-point. The larva 

 of Stratiomys is of remarkably elongate, strap-like, form, much 

 narrowed behind, with very small head ; the terminal segment 

 is very long and ends in a rosette of hairs which the creature 

 allows to float at the surface. After the larval skin is shed the 

 pupa, though free, is contained therein ; the skin alters but 

 little in form, and has no organic connection with the pupa, 

 which merely uses the skin as a shield or float. These larvae 

 have been very frequently described ; they can live out of the 

 water. Brauer describes the larvae of the family as " perip- 

 neustic, some perhaps amphipneustic.'' Miall says there are, in 

 Stratiomys, nine pairs of spiracles on the sides of the body which 

 are not open, though branches from the longitudinal air-tubes 

 pass to them. There are probably upwards of 1000 species of 

 Stratiomyiidae known, and in Britain we have 40 or 50 kinds. 

 The American genus Chiromysa, Wied., was formerly treated by 

 Osten Sacken as a separate family, Chiromyzidae, but Williston 

 places it in Stratiomyidae. 



Fam. 14. Leptidae, including Xylophagidae and Coenomyi- 

 idae. — The Leptidae proper are flies of feeble liuild ; antennae 

 with three joints and a terminal bristle ; in the Xylophagidae the 

 antennae are longer, and the third joint is complex. The ivings 

 have five posterior cells, the middle tihiae are spined. Pulvilli and a 

 piulvilliform empodium present. The three families are considered 

 distinct by most authors, but there has always been much difficulty 

 about the Xylophagidae and Coenomyiidae, we therefore treat them 



