DIPTBRA— BIBIONID^, 583 



slender and the insect minute ; the proboscis is about as long as the head 

 and thorax combined, and the last joint of the equally long palpi is cuneate, 

 the base rounded. 



Length of body, 2.2"""' ; of proboscis, 0.9""°. 



Fossil Canon, White River, Utah (W. Denton). 



CORETHRA Meigen. 



CORETHRA EXITA. 



PI. 5, Pigs. 22, 23. 



Corethra exita Scudd., Bull. U. S. Geol. Geogr. Surv. Terr., Ill, 744 (1877). 



A specimen, viewed from above, with expanded wings, and destitute of 

 legs, palpi, and all but the basal joints of the antennae. The broad head, 

 stout basal joint of antennje, general form and size, with such of the neura- 

 tion of one wing as can be determined, indicate the genus ; seven of the 

 abdominal segments are very clearly marked, and the specimen appears to 

 be a male. The body is slender ; the head, thorax, and abdomen of equal 

 width ; the wings slender and of about equal length with the body. The 

 fourth longitudinal vein runs in a nearly straight line over the basal half of 

 its course, but is gently arched beyond ; the fifth originates from the fourth 

 in the middle of its straight portion, runs nearly parallel with it so long as it 

 continues straight, and afterward diverges considerably; the first longitudinal 

 vein appears to run to the tip of the wing-. 



Length of body, 4.25""" ; of wing, 4.25'"'" ; breadth of latter, 0.8""'. 



Chagrin Valley, White River, Colorado. One specimen (W. Denton). 



Family BIBIONID^E Westwood. 

 PLECIA Wiedemann. 



Plecia similkameena. 

 PI. 3, Figs. 20-22, 



Penthetria similkameena Scudd., Rep. Progr. Geol. Surv. Can., 1877-1878, 177-179B (1879). 

 Plecia similkameena Scudd., Zittel, Handb. d. Palseont., I, ii, 811, Fig. 1086 (1885). 



Five specimens, three of them with their reverses, represent very fairly 

 a species of Plecia, one of them certainly a male, and remarkably perfect. 

 The body of this male is of nearly equal size throughout, scarcely thickened 



