2 BULLETIN 116, UNITED STATES NATIONAL MUSEUM. 



The first antennal joint is hairy above; the vertex not much hol- 

 lowed, never obliterated by the approximation of the eyes; thorax 

 slightly compressed, rather high in front, with short, rounded scutel- 

 lum; abdomen also someAvhat compressed, the male hypopygiiim 

 long, bent forward under the venter. Hind cross-vein about in tlje 

 middle of the wing field (disregarding the narrow basal portion); 

 fourth vein rather strongly bicurved beyond it, rarely with one or 

 both of the curves extending into a short stump, ending in or more 

 often well before the apex. The accompanying figure (fig. 1) shows 

 well the general characters. 



For purposes of classification the characters fall very readily into 

 two groups, those which occur only in the male and those which 

 occur in both sexes. Of the former there are very many, and in 

 general they are easy to see and very striking; hence the males are 

 much easier to identify than the females. Characters available for 

 both sexes are color of legs and antennae; color of the infra-orbital 

 cilia — a row of erect small hairs behind the eye, the upper ones of 

 which are always black; color of the cilia of the calypters — delicate 

 outstanding hairs on the little padlike organ just below and behind 

 the wing; usually the venation; and some others. 



Male characters occur in many places; the antennae may be elon- 

 gated or swollen, the arista may have the appearance of a spearhead 

 at apex, the face may be bright silvery or pm-e brown in its pollen, 

 and elongated below; the front tarsi may be long or short in various 

 joints, and often are compressed and enlarged on the apical one, two, 

 or three joints, which may be white, black, or silveiy; the front 

 empodia may be plumelike; the middle tarsi or even the hind ones 

 may be ornamented instead of the front ones; the tibiae sometimes 

 partake of the ornamentation of their tarsi; the hind femora may 

 bear long cilia below, light or dark; the costa may be variously 

 thickened; the apical half of the wing may contain a distinct black 

 spot or a dark shade; and the posterior margin of the wing toward the 

 base is often excised, emarginate or lobed. There are a few other 

 characters of this class. The lamellae of the hypopygium have 

 numerous peculiar modifications. 



Most of these characters are distinctly of the nature of male orna- 

 ments. In several cases the male has been observed to display them 

 before the female verv' assiduously. In the American Naturalist,' 

 I described the behavior of Dolichopus tenuipes Aldrich (it was then 

 an undescribed species) and of D. crenatus Osten Sacken. I quote 

 these observations in order to bring together all the information that 

 I have relating to these habits in the genus: 



[DoUchopus tenuipes Aldrich] has the fore tarsi in the male exceedingly elongated 

 and slender, with the last joint in the shape of a comparatively large, oval black disk 



I Vol. 28, 1894, 35-37. 



