576 GEOLOGICAL SURVEY OF THE TERRITORIES. 



Habitat. — Foot-hills, Colorado, September, and mountains on the 

 Pacific slope, August 16 to September 6. Several specimens in alcohol. 



This genus is new for the American fauna ; all species known belong 

 to Europe and Siberia. This^new species is far more interesting as an 

 exception, bearing gills in the imago-state. There are on the ventral 

 side five pairs of gills, formed by white, fleshy, blind sacs ; two pairs on 

 the under side of the head ; the first pair widely separated on the basal 

 part of the submentum ; the second pair in the articulation with the 

 prothorax ; both pairs straight, placed transversely, looking outward. 

 The three other pairs on the thorax, always before the feet, but sepa- 

 rated from them, being placed just in the articulation of the segments ; 

 the three thoracic pairs are incurved. 



The occurrence of gills in the imago-state of D. signata is the more 

 exceptional, as all the hitherto-known species are without them. At 

 least, a close examination of dry specimens of all the species in my col- 

 lection (only one of Siberia is unknown tome) did not disclose anything 

 similar to the gills in B. signata ; Dr. Gerstaecker, in a recently-pub- 

 lished paper, also states the absence of gills in living specimens of Z>. 

 intricata and JJ. alpina. Formerly, the genus Pteronarcys was the only 

 known exception for its gill-bearing imagos among the class of insects ; 

 now, besides the above-described Bictyopteryx^ there are two other gill- 

 bearing Perlid genera mentioned by Dr. Gerstaecker, Baniphipnoa 

 lichenalis from Ghili, a genus closely related to FteronarcySj and Nemura 

 cinerea and N. nitida, with its male N. lateralis, both from Europe. 



The papers by Dr. Gerstaecker are published in the Festschrift sum 

 liundertjaehrigen Bestehen der Gesellscha/tnaturforschender Freunde, Berlin, 

 1873, 4to, p. 60, with figures; and Sitsungshericht derselben Gersellschaft, 

 October 21, 1873, p. 99. 



ISOGENUS. 



I. elongatus, sp. nov. 



Female. — Brown ; head with a posterior, triangular, yellow spot, 

 extended on each side of the occiput ; two small, ill-defined, yellow spots 

 near the antennae and eyes ; antennas brown. Prothorax as broad as 

 the head, quadrangular ; the angles sharp, with a large, yellow, median 

 band, narrower before. Abdomen and feet brown 5 setae brown ; base 

 of the joints paler. Wings long, hyaline ; veins brown, with a pale- 

 yellow tinge around the costal apical veins ', costa pale ; submedian 

 areolet larger toward the tip, with seven transversal veins ; the ante- 

 rior vein of the submedian areolet somewhat curved. Vulvar lamina 

 large, the base separated from the segment by a deep furrow in form of 

 a transversely-enlarged W ; apical margin nearly straight, covering 

 only a little of the following segment ; the lateral angles rounded ; a 

 small notch in the middle. 



Length, with the wings, 24-28 millimeters. Alar expansion, 40-44 

 millimeters. 



Habitat — Foot-hills, Colorado (Mr. Carpenter) ; Ogden, Utah (by C. 

 Thomas). Alcoholic specimens. I. elongatus is very similar to I. fron- 

 talis, but in this species the anterior vein of the submedian areolet 

 js straight, and the anterior margin of the vulvar lamina rather incurved. 



I. colubrinus, sp. nov. 



Brown ; head with a posterior, triangular, yellow spot ; part before the 

 ocelli yellowish ; antennae blackish-brown ; prothorax rather smaller 

 than the head, quadrangular; angles sharp, with a yellowish median 

 band, a little narrower before ; abdomen and setae dark- brown ; feet pale- 

 brown, tips of the femora and tibiae darker. Wings hyaline; veins 



