144 ERNEST A. BACK. 



The front, like the face, presents much variation. It may 

 be very narrow and of equal width (Leptogaster) , very much 

 widened above (Townsejtdia) , or strikingly narrowed above so 

 that the eyes approach a condition of contiguity found in no 

 genus but Plesiomma. In Townsendia, the front and vertex 

 occupy a large portion of the upper part of the head. The 

 vertex is usually well depressed and the ocellar tubercle, bear- 

 ing the three ocelli, quite prominent. 



The mouth parts form a stout, firm, horny proboscis without 

 fleshy labella at the tip. It may be very short {Holcocephala), 

 or comparatively long (Microstylum). The palpi are of var- 

 iable length but never prominent, single jointed in the Lep- 

 togastrinae and Asilinae, two jointed in the Dasypogoninag and 

 Laphrinae. 



The antennae present many characters of generic and specific 

 importance; of these one may obtain a fair idea by referring 

 to Plates III and IV. The variations in size, shape, and 

 clothing, are too numerous to receive special attention at 

 this point. In general, the antennae are divided into three 

 distinct segments; the third segment distally with or without 

 a terminal style or bristle. The two basal segments are 

 always comparatively short, cylindrical, sometimes more 

 rounded; the third is usually longer than the basal two taken 

 together, and presents a considerable variety of form. The 

 style present in nearly all the genera, may be distinctly sep- 

 arated from the third segment, or hardly so (Holcocephala and 

 Dioctria); it may be long and slender (Holopogon) , stout and 

 short (PsilocurMs), or greatly elongated and apparently form- 

 ing distinct antennal segments {Ceraturgus) . With few excep- 

 tions, under the compound microscope, the style will be found 

 to be two-jointed, usually the basal segment being very short 

 and the second segment long and slender (Nicocles), or the 

 opposite may be true (Stichopogon) , while again both segments 

 may be short and stout (Laphystia) . The terminal segment 

 of the style may bear a terminal bristle of its own (Laphystia) 

 or a lateral bristle {Ceraturgopsis) . 



The head, as the rest of the body, is variously clothed with 

 bristles and pile, and the ground color is more often obscured 



