420 The University Science Bulletin. 



of Comb Ridge, where the road from Bluff to Goodridge enters 

 Comb Wash. Some vegetation was growing about the spring. 



To the above Utah collections may be added this interesting one 

 from northwestern Colorado, made in 1920. 



junction mountain, YAMPA river, northwestern COLORADO. 



In the deep canyon of Yampa river, where the river plunges 

 through Junction mountain, about thirty-five miles east of the con- 

 fluence of the Yampa and the Green, in northwestern Colorado, were 

 taken forty-four Rhagovelia distincta Champ., all apterous; nine 

 were males, four nymphs, and the remainder females; also seven 

 Trepobatopsis trux Bueno, two males and five females, described by 

 Mr. Bueno as new. 



From a small, sluggish stream at west side of Junction mountain 

 were taken an interesting series of large gerrids. These vary in 

 color from russet to the dark color typical of Gerris remigis Say. 

 The russet-colored form has been determined by Mr. J. R. de la 

 Torre Bueno as Gerris orba Stal. Of these there are nineteen speci- 

 mens, nine males and ten females. Thirteen of the lot are apterous. 

 G. orba Stal has been listed from California, Oregon and Nevada 

 hitherto. The others, forty-seven of them, all apterous, are of a 

 trifle lighter color than G. remigis Say, but obviously are the same 

 as Bueno's orba. 



In an attempt to find differences between our common Gerris re- 

 migis Say and this series from the West, all of the Kansas and Colo- 

 rado material available (a series from the eastern margin of Kan- 

 sas through the state and across Colorado) has been very carefully 

 studied. The Kansas forms are darker and larger as a series, but it 

 does not seem possible at the present time to fix upon any structural 

 characters to distinguish these forms. 



In connection with the problem of separating the striders, it may 

 not be out of place to state that it seems to have been overlooked 

 that Gerris conformis Uhl. males have the ventral side of the sixth 

 abdominal segment singly emarginate, like Limnoporus rufoscutel- 

 latus Latr. Indeed, the two species have, in addition to the above 

 genital character, another distinctive character that is common to 

 both, namely, their very long legs. The hind femora in both spe- 

 cies greatly surpass the tip of the abdomen. The examination of 

 such material as has been available suggests that the two species 

 commonly accepted as L. rujoscutellatus and Gerris conformis Uhl. 

 may be separated as follows : 



