226 



rudiment to a length equalling two or three times that of the 

 abdomen. Frequently the long and short winged forms differ 

 eonsiderably in color and proportions, and the sexes are often 

 very dissimilar. 



Some of the most available characters for distinguishing 

 the genera are the following: — The form of the antenna;, 

 whether flattened or terete, and the proportionate length of the 

 joints; the form of the front and vertex; the number of carinae 

 on the front, pronotum and scutellum ; the point of forking of 

 the median carina of the front, and the direction taken by those 

 on the sides of the pronotum. In the large genus Libumia ex- 

 cellent specific characters are found in the form of the genital 

 segment of the male. When viewed from behind we distin- 

 guish the form of the aperature of the pygofers — The two pieces 

 which, united above and below, form the wall of the genital 

 segment. Dorsally these are notched to receive the anal tube 

 and on the central aspect there is generally a sinus to receive 

 the base of the stiles. These stiles are very variable in form in 

 the different species but usually they are rather slender, curved 

 outward more or less and convergent above toward the anal 

 tube. The inferior wall of this anal tube is frequently produced 

 in a more or less prominent incurved tooth on each side of the 

 median suture. In the females the form of the pygofers varies 

 somewhat as well as the proportions of the oviduct. 



Thirty-two species and three genera are described as new 

 in the present paper, making the number of species now record- 

 ed from North America, excluding known synonyms, fifty 

 three, representing thirteen genera. Of these fifty three species 

 eleven have not been positively identified by the writer and 

 four were previously described from Europe. 



No attempt has been made in the preparation of this paper 

 to obtain all the material in this country that is available for 

 study. Had this been done the number of species certainly 

 would have been largely increased. But even in this fragmen- 

 tary form it is hoped that these studies will be of some service 

 as placing on a more systematic basis some of our more common 

 forms. A large field for original work is open here to some 

 student who has the time and perseverance to work out the 

 affinities of these minute insects. 



