14 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.60. 



since then all American authors have followed this synonymy. There 

 seemed to be no good reason for doubting that the American species 

 was the same as the European and the writers* were much surprised, 

 when they compared American insects with literature and European 

 specimens, to find that isomerus did not agree with pcctinicomis. 

 Isomerus diifers from pectinicoimis in much the same manner as does 

 the European di/formis, and if the American species is the same as 

 any Euroj)ean species it is synonymous with difformis, and not pectiiii- 

 cornis, as previously supposed. The United States National Museum 

 contains about fifteen specimens of Cladii from the Palearctic region, 

 and while most of these agree with various species as they are 

 characterized, some few, especially specimens from Japan, do not 

 agree, and it seems that the understanding of the species in Europe 

 is not yet sufficiently stabilized to make it advisable to try to synony- 

 mize our American species with any of the European. Until it is 

 possible to carefully compare our American form with authentic 

 European specimens of all the species we prefer to use Norton's 

 name for our species. We have studied very many specimens, col- 

 lected throughout the range of the species in America, and have ob- 

 served but little variation. The absence of variation in the number 

 of rami on the male flagellum is especially noticeable. The extent 

 of yellow on the legs is also remarkably constant. 



Feviale. — Length 5 to 6 mm.; length of antenna about 3 mm. 

 Clypeus coarsely punctured, convex, the anterior margin broadly, 

 arcuately emarginate, the lobes narrow and triangular in outline; 

 supraclypeal foveae deep, oval in outline; lateral supraclypeal area 

 convex near the eye, sharply sloping into the antennal foveae ; ocellar 

 basin completely wanting; frontal crest strong, broken medianly; 

 middle foveae small, oval in outline; postocellar line nearly twice as 

 long as the ocellocular line; ocellocular line slightly longer than the 

 ocelloccipital line; antennal furrows wanting; postocellar furrow 

 complete, well defined, straight, not broken by the furrow from the 

 anterior ocellus; postocellar area sharply defined laterally, very 

 gently convex ; antenna as in figures 17 and 28 ; wings as in figure 7 ; 

 sheath straight above, truncate apically, oblique to the broad base; 

 ovipositor as in figures 39 and 45; cerci long, slender. Black; tibiae 

 and tarsi white; apices of the posterior tibiae and the apical four 

 joints of the posterior tarsi brownish ; wings yellowish hyaline ; vena- 

 tion pale brown, costa and the stigma j^ellowish, 



Male. — Length 5 mm. The above description of the female ap- 

 plies very well to this sex except that the four anterior tarsi are 

 usually brown and the costa is not so distinctly yellowish; hypopy- 

 gidiun narrowly rounded; antenna as in figures 16 and 29. 



Described from numerous specimens taken in the vicinity of Wash- 

 ington, District of Columbia. 



