ACIIALCUS. 21 1 



which, on account of its shortness, is difficult to perceive ; on 

 their exterior side some short white little hairs are also inserted; 

 one of the uppermost, however, is sometimes of a black color. 

 The fore femora, which are moderately thickened towards the root, 

 have, on their under side, a dense row of very short, straight, 

 erect little bristles, and near the basis two or three longer bristles. 

 The under side of the fore tibiae is also provided with a dense 

 row of very short small bristles. Tarsi black. The halteres 

 appear to be black. Wings long, tinged with a gray-blackish 

 color, not darker towards the anterior margin, and up to the ex- 

 treme root with black veins ; the end of the fourth longitudinal 

 vein is completely parallel to the third ; the posterior transverse 

 vein is perpendicular, without dark margin and dark spot upon its 

 middle ; the convexity crossed by the last segment of the fourth 

 longitudinal vein is not darker than its surroundings. 

 Hab. Pennsylvania. 



Gen. XXXVIII. ACHALCUS. 



Characters. Color non-metallic. The first joint of the an- 

 tennae glabrous, the third pointed-ovate ; the long and slender 

 arista subapical. Face narrow. Abdomen with six segments in 

 both sexes ; the female abdomen at the end without a coronet of 

 bristles. Hypopygium small ; its exterior appendages have the 

 shape of small lamellae. The first joint of the hind tarsi without 

 bristles, shorter than the second. The sixth longitudinal vein of 

 the wings is wanting. 



It is impossible to overlook the relationship of the genus 

 Achalcus with the four following genera, which are distinguished 

 by the posterior end of the thoracic dorsum being provided with 

 a concave area. 



This relationship is also illustrated by the want of the coronet of 

 bristles on the posterior end of the female abdomen, which Achalcus 

 has in common with these four genera. I have only a few speci- 

 mens of Achalcus JiavicoJUs in my possession; the manner in 

 which they are pinned renders it impossible to ascertain whether 

 the posterior end of the upper side of the thorax has a concave 

 surface or not ; it seems to me that the latter is the case. 



The name of the genus (from a, non, and ^axxoj, brass) has refer- 

 ence to the non-metallic color of the species. 



