892 Charles Paul Alexander 



G. canadensis is most commonly found along small streams near cliffs; 

 G. diversa, restino; on vegetation along running water or clinging to vertifvl 

 wet banks; G. rostrata, on rich vegetation in damp j)laces, where it is often 

 extremely abundant (Alexander, 1912:67-68). The habits of the adult 

 flies are discussed on page 878. 



Genus Discobola Osten Sacken 



1865 Discobola 0. S. Proc. Ent. Soc. Phil., p. 226. 



1869 Trochobola O. S. Mon. Dipt. N. Amer., part 4, p. 98. 



The genus Discobola is a well-defined group including eight described 

 species with a curious discontinuous distribution — two species occurring 

 in North America, two in Europe, and four in New Zealand. The species 

 are readily distinguished by the presence of a strong supernumerary 

 cross-vein between the two anal veins. The only local species is D. 

 argus. 



Discobola argus (Say) 



1824 Limnobia argus Say. Long's Exped., App., p. 358. 

 1865 Discobola argus O. S. Proc. Ent. Soc. Phil., p. 226. 



The species Discobola argus is a curious fly, with ocellate markings on 

 the yellowish white wings (Plate XXXII, 41). The body coloration is 

 yellowish, the thorax with three brown stripes, each femur with a brown 

 subterminal ring. The immature stages of the American species are 

 unknown but are probably spent in decaying pine stumps, as are those 

 of the European D. caesarea; specimens of D. argus have been observed 

 mating on the bark of stumps (in Ithaca, New York, October 3, 1912, 

 by Ilg and Alexander). The fly is uncommon in May and June but 

 becomes more numerous from August to October. 



Genus Rhipidia Meigen 



1818 Rhipidia Meig. Syst. Beschr., vol. 1, p. 153. 



In the genus Rhipidia there are about twenty-eight described species, 



most numerous in the tropics of the New World. The character of the 



pectination of the antennae (page 851) varies in the different groups or 



subgenera as follows: 



Rhipidia Meig. (rnaculata, hryanti) — antennae of the male bipectinate. 



Monorhipidia Alex, (fidelis) — antennae of the male unipectinate. 



Arhipidia Alex, {domeslica, shannoni) — antennae of both sexes subpectinate to simple. 



