FIELD BOOK OF INSECTS. 



The families of CALYPTERATE Diptera are very 

 difficult, even for specialists, but, on account of the im- 

 portance of some of the Muscidae, an effort must be made 

 to enable intelligent non-specialists to recognize a few of 

 the species. Differing from ACALYPTER^ (see p. 274), 

 these flies have well developed squama?; the auxiliary 

 vein is always distinct throughout; the first longitudinal 

 vein is never very short; the eyes of the males frequently 

 touch; the thorax has a complete transverse suture; and 

 the flies are never very small. 



The technical terms, about to be used, are explained on 

 p. 230 and Plate LXIX, except " hypopleura, " the space on 

 the side of the thorax above the hind coxae, and "bucca, " 

 the cheeks, below the eyes. It should be remembered 

 that the keys will work only with the flies for which they 

 are intended; if you apply them to some other creature, 

 you will get weird results. 



Since it is the Muscidae which are of principal interest, 

 it should be noted, when at 5, that Lucilia sylvarum has a 

 pair of bristles on the posterior margin of the second 

 abdominal segment but its legs are not noticeably long; 

 when at 6, the Muscid genus, Muscina, may give trouble 

 as the narrowing of the posterior cell is not very pro- 

 nounced. 



1. Mouth-opening small; mouth-parts small or ves- 

 tigial (EsTRiD^: (p. 259). 



Mouth-opening normal; mouth-parts not ves- 

 tigial 2. 



2. Hypopleurae with a tuft of bristles 3. 



No tuft of bristles on the hypopleurae 6. 



3. Antenna! bristle (arista) bare or only slightly pu- 

 bescent TACHINHXE (p. 260). 



Arista plumose or very distinctly pubescent 4. 



4. Arista bare on the distal (outer) half . . SARCOPHAGID^E 

 (p. 262). 



Arista plumose or distinctly pubescent to tip 5. 



5. Back of abdomen usually bristly on the anterior 

 part; legs usually long DEXIID^E (p. 260). 



No bristles on front part of back of abdomen; legs not 

 noticeably elongated Some MUSCIDAE (p. 266). 



258 



