HORSE-FLIES AND WESTERN AGRICULTURE. 17 



third, dorsal, with strongly chitinized concave, crescent-shaped marginal thick- 

 ening, possibly lacinia. Maxillary palpus 3-jointed ; all joints subequal in 

 length, basal joint almost square, twice as wide as second, and second joint 

 twice as wide as the apical one. Mentum, submentum, and basal region of 

 labium representing stipes labii and palpiger labii, fused into a small, trans- 

 verse, entirely membranous area in front of the gular plate and between the 

 posterior parts of the cardines (F). 4 Labial palp small, with two yellowish, 

 chitinized joints ; basal joint very low, twice as wide as apical joints ; apical 

 joint comparatively long, cylindrical, slender, about same length and width as 

 the apical joint of the maxillary palpus. Ligula as long as gular plate, half 

 as wide ; white and entirely membranous ; apically bifid, forming two glossse. 

 The paragnaths of Snodgrass and Crampton (=the niaxillube of H. I. Hansen 

 and G. H. Carpenter =the paraglossse auctorum) present behind the dorsal 

 or buccal surface of glossre ; each paragnath forming a chitinized, small, well- 

 defined sclerite, standing up as a longitudinal, short, triangular, compressed 

 tooth (E). The buccal floor smoothly chitinized between the paragnaths. The 

 hypopharyngeal chitinization anteriorly fused with the floor chitinization, but 

 rising to a somewhat higher level ; prolonged into a single, dorsally concave, 

 ventrally convex rail which extends backward through the cranial cavity above 

 the oesophagus and to which strong retractor muscles are attached. Epi- 

 pharynx distally formed by a slightly chitinized, elongate-subovate minor part, 

 proximally by a rodlike, anteriorly upward-curved major part. This latter 

 part joins with the hypopharyngeal chitinization above the entrance to the 

 oesophagus and at the point where the rail-shaped internal chitinization begins. 



Segments of thorax and abdomen. — Prothorax and 8th abdominal segment 

 conical with obtuse apices, respectively pointing forward and backward, subequal 

 both in length, about 2 millimeters, and in width, about 1.75 millimeters. Meso- 

 thorax and metathorax subequal in size and general shape to the 7 anterior 

 abdominal segments, each about 5 millimeters long and about 5 millimeters wide. 

 Segments, in parts finely longitudinally striate, white anteriorly with a rather 

 conspicuous dark girdle containing white spots corresponding to muscle at- 

 tachments on the inside; metathorax and abdominal segments also with pos- 

 terior dark, but less conspicuous, girdle. On each thoracic segment the border 

 between the dorsal and lateral regions is marked by a dark, longitudinal, 

 posteriorly pointed stripe froni the anterior girdle ; a similar marked border be> 

 tween the lateral and ventral regions; in the prothorax the lateral region is 

 uniformly colored without any median longitudinal stripe, in the mesothorax 

 and metathorax 2 such stripes are present (M) ; in the prothorax the ventral 

 region has a single median longitudinal stripe, in the mesothorax and meta- 

 thorax no ventral stripes. Abdominal segments without stripes, but located in 

 the anterior girdle, dorsally with one low ampulla on each side, laterally with 

 one large ampulla, ventrally with two large ampullae. Ampulla? reduced in the 

 eighth segment. 



Spiracles. — Thoracic spiracles, one pair, very small, usually concealed within 

 a vertical cleft, located laterally in the segmental boundary line between the pro- 

 thorax and mesothorax. Abdominal spiracles, one pair, large, with a vertical 

 spiracular slit, placed closely together at the end of a telescopically movable, 

 posteriorly protruding, dorsal prolongation of the eighth abdominal segment. 



Pupa. 5 



The pupa (fig. 14, A, B; PI. I, E) is 28.5 to 33 millimeters long. The width of 

 the thorax is 6 millimeters. Just after transformation the pupa is pale yellow- 

 ish throughout. When nearing transformation to adult, the head turns black, 

 and under the binocular the eye facets may be plainly seen through the skin. 

 Dark areas also appear upon the prothorax, and the entire body is somewhat 

 darker. 



The head portion bears at the lower extremity of the anterior aspect, ar- 

 ranged upon opposite sides of the median line, two rounded, wedge-shaped, 

 chitinous projections. Immediately laterad of these is a prominent tubercle, 

 evidently the palpal sheaths. Posterior to the wedge-shaped teeth and some- 

 what remote from them are 2 prominent rounded chitinous tubercles, 1 at each 



4 The gular plate of the orthorrhaph larvae has by recent authors been termed " sub- 

 mentum " ; this interpretation is not correct, as the submentum always is located in 

 front of the posterior end of the cardines, the gula behind. 



5 Description by J. L. Webb, Bureau of Entomology. 



67887°— 24 2 



