108 INSECUTOR INSCITI^ MENSTRUUS 



series 1, no change has occurred. In series 2, fletcheri has as- 

 sumed a yellow color and become indistinguishable from 

 riparius, with which it flies in the Canadian prairies, while 

 cantator has the markings dulled and the tarsal rings nar- 

 rowed, till it closely resembles the wholly unrelated vexans 

 Meigen. This in adaptation to its salt-marsh habitat. In 

 series 3, riparius has become yellow, as noted above, while 

 grosshecki and squamiger have acquired distinctive enlarged 

 wing-scales, upon which an author was induced to found a 

 genus. ^ Of these two, grosshecki maintains a precarious ex- 

 istence in the east along the Atlantic region, while squamiger 

 is a salt-marsh form of the Pacific coast, to which habitat it 

 has frankly abandoned itself, in larval structure as well. 



In the following table, based on the male hypopygium, the 

 first insert indicates the series, the second the species, the third 

 the subspecies, under which latter heading the forms will be 

 discussed. 



Basal lobe of the side piece without a spine or tuft of setae, flat; apical 

 lobe with short normal setae, pointed inwardly (series 1). 



1. Rugose area of basal lobe reaching up to apical lobe, 



excrucians Walker 



2. Rugose area of basal lobe not reaching beyond middle of side- 



piece. 

 Filament of claspette angularly expanded beyond middle ; 



spines of ninth tergites longer increpitus Dyar 



Filament of claspette angularly expanded toward base; 



spines of ninth tergites shorter mutatus Dyar 



Basal lobe with a strong distinct spine, free, accompanied by few setae; 

 lobe flat; apical lobe with normal setae, pointed inward (series 2). 



3. Basal lobe rugose nearly to apical lobe ; filament of clas- 



pette angularly expanded at basal third fletcheri Coquillett 



4. Basal lobe round, not longer than broad, rugose ; filament 



of claspette expanded at middle. 

 Setae of apical lobe coarser than the ordinary vestiture, 



mississippii Dyar 

 Setae of apical lobe about the same size as the vestiture, 



classicus Dyar, stimulans Walker 

 Setae of apical lobe distinctly weaker than the vestiture, 



alberta Dyar 



^ Lepidoplatys Coquillett, Science, n. s., xxlii, 314, 1906. 



