410 



36. Small species, 2 mm. in length ; colors (of enclosed imago) black and 

 yellow Cricotopus exilis*. 



— Larger species, 2.5-3 mm. in length; color (of enclosed imago) fus- 

 cous green OrfJiodadius fugax*. 



DiAMESA Meigen 



This genus may be distinguished from any other in ChironomincB 

 by the presence of the medio-cubital cross vein of the wing. From 

 the genera in Tanypincc it may be distinguished by the 8-jointed an- 

 tennae of the female and also by the distinctly chironomine type of 

 larva. 



One species has been found in Illinois, descriptions of all stages of 

 which are given herewith. 



DiAMESA WALTLII McigCn 

 Biamesa icaltlii Meigen, Syst. Besehr. Eur. Zwiefl. Ins., Vol. 7, 1838, p. 13, sp. 1. 



Larva. — Length, 8-io mm. Pale green. Head brownish on pos- 

 terior margins and apices of mandibles. Mandibles with five teeth; 

 labium as in Figure 3, Plate XXIX, its apex very slightly darkened. 

 Thoracic and anal pseudopods present, the former with apical hairs, 

 the latter with distinct claws as in Chironomus; dorsal blood-gills four 

 in number ; anal blood-gills absent. 



Pupa. — Length, 7-8 mm. Dark brown. Thoracic respiratory 

 organs very small. Segments 2-7 of abdomen with a transverse row 

 of about twelve small toothlike setulse on the posterior margin; apex 

 of abdomen with six distinct straplike filaments. 



Imago; Male. — Black, slightly shining. Head and its members 

 black ; antennal plumes dark brown. Thorax with distinct gray prui- 

 nescence, which is most conspicuous beween the vittae on mesonotum. 

 Abdomen with posterior margins of segments gray pruinescent. Legs 

 entirely fuscous. Wings slightly grayish, veins dark brown. Halteres 

 yellow. 



Palpi long, 5-jointed, the basal joint, as usual, very short, the next 

 shorter than the third and fourth, apical joint longest. Hairs on 

 mesonotum confined to the areas between the vittse ; scutellum rather 

 densely haired; pronotum broad, continued almost to upper margin of 

 mesonotum, a distinct notch in its center. Hypopygium as in Figure 

 II, Plate XXIII. Legs slender; fore tibia one and a half times as 

 long as basal joint of fore tarsus; fourth tarsal joint of all legs 



*I can find no structural characters mentioned in Johannsen 's descriptions of 

 ■ C. exilis and 0. fugax by means of which the species may be separated. 



