252 NEW YORK STATE MUSEUM 



Imagines 

 a At least the apical half of the middle and hind femora black 



h Abdominal segments with narrow white posterior margins ; fore 

 metatarsus about one fourth or one third shorter than its tibia 



1. tremulus 

 hb Abdomen with wide white or yellow fasciae 



c Abdomen with the first, most of the third, half of the fifth, and 

 posterior margins of the second and the fourth, yellow 



2. geminatus 

 cc Abdomen not mai'ked in this manner 



d With the foi'e metatarsus about one half as long as the tibia 

 e With yellow bands on the first, fourth and seventh segments 



3. trifasciatus (var. tricinctus) 

 ee With yellow bands on the first, fourth and fifth segments 



4. e X i 1 i s n. sp. 

 (Id With the fore metatarsus about two thirds as long as its tibia 

 e With yellow bands on the first and fourth segments 



5. bicinctus 

 ee With the first and second wholly, and a part of the third and 



fourth segments yellow 6. v a r i p e s 



aa Middle and hind femora for the most part yellow or white 

 b With first, fourth and seventh abdominal segments yellow 



3. trifasciatus 

 bb Abdomen not marked in this manner 



c Metatarsus of the fore legs about one half as long as the tibia ; 



abdominal segments with yellow margins 7. sylvestris 



cc Fore metatarsus about two thirds as long as the tibia ; abdominal 



segments with brown posterior bands 8. debilis 



Note. — Consult also the auxiliary key containing Walker's species, p.l98. 



In occasional specimens of some members of this genus the 

 part which is usually yellow is found to be black. In this case, 

 however, the black is shining, and easily contrasts with the vel- 

 vet black of the other parts. 



1. Cricotopus tremulus Linne 



1758 T i p u 1 a Linn. Syst. Nat. ed. X. p.5S7, 23 



1767 T i p u 1 a Linn. Syst. Nat. ed. XII. p.975, 31 



1804 Chironomus Meigen. Klass. 1:15,11 



1818 Chironomus Meigen. Syst. Beschr. 1 : 45, 56 



1850 Chironomus Zett. Dipt. Scand. 9 : 3562, 88 



1864 Chironomus Schiner. Fauna Austr. 2 : 611, 72 



1884 Cricotopus Mik. Wieii. Ent. Zeitg. 3 : 202 



1899 Cricotopus .Tolinsnn. in Smith's Cat'l. Ins. N. J. p. 627 



Male. Dorsum of tlio thorax yellow, with wide, posteriorly 

 confluent longitudinal shining black stripes; the pleura some- 

 times paler with black spot at the base of the wing; the scutel- 



