72 THOMAS SAY FOUNDATION 



nute outwardly directed prickles, and with its slender apex 

 curved posteriorly in a small hook. There is also a sharp 

 thorn-like spine pointing rearward from base of cap. In 

 all this it is very similar to /. frontalis and /. colubrinus, but 

 the terminal decurved tip appears to be less hooked than 

 in those species, and the lateral stylets are a little longer, 

 their tips reaching the level of the base of the terminal 

 hook. The lateral stylets are half as long as the entire 

 supra-anal process, stout, nearly straight, simple, blunt 

 on apex, their distal third covered with microscopic den- 

 ticulations in concentric lines. 



Female. The subgenital plate is variable, but generally 

 it is truncated squarely and bears a minute median notch, 

 though this notch in some specimens is lacking. 



Distribution. — Foothills of Colo, and Ogden, Ut. (fe- 

 male type and cotypes) ; Poudre River, Colo., June (U. S. 

 N. M.) ; Platte Canon, Colo., May (Dyar and Caudell) ; 

 Montana Exp. Sta., Bozeman, Mont., May, 1920; Gallatin 

 Co., Mont., May 23, 1917. Elevation 4,800 feet (R. A. 

 Cooley). 



Isogenus colubrinus Hagen. 



(Plate 10, figs. 11, 18; plate 11, fig. 5.) 



L875. Isogenus colubrinus Hag., Bull. Geo!. Surv. Terr., p. 576. 

 1907. I. •stm i' a ns ml itb rimis Banks, Cat. Neurop., p. 11. 

 1912. Isogenus colubrinus Klap., Coll. Selys, 4:59. 



Length to wing tips, male, 18-20 mm.; female, 22-23 

 mm. Expanse, male, 26-32 mm. ; female, 28-44 mm. 



Color brown, with a middorsal stripe of yellow on the 

 prothorax. Head brown, with a triangular yellow spot on 

 the occiput, that sometimes extends forward between the 

 ocelli. The transverse M-mark across the frons is pol- 

 ished, and its angles are all rounded off. At its outer end 

 is a pair of pale spots near the antennae. Ocelli minute 

 and spaced as in /. frontalis. Antennae and palpi brown. 



Prothorax a little wider than long, rectangular with 

 sharp angles ; median yellow stripe widened at the front 

 margin, and again toward the rear. Legs brown, dark- 

 ened toward the knees, except for the usual pale line 

 across the tip of each femur. Wings subhyaline, veins 

 brown, with costal and subcostal veins a little paler than 

 the others, a very slight darkening of the area about the 

 front of the cord. 



Abdomen brown: Tails brown except at base where 

 they are yellowish, as are the subanal plates. The male 

 genitals are very similar to /. frontalis: the genital hooks 

 of segment 10 appear to be a little shorter; the pad-like 



