48 JOHN B. SMITH. 



i 



type is found. Ou the secondaries vein 8 may arise from the root 

 or from the subcostal, and if the former it may reunite with the 

 subcostal to form a loop at base, or it may run entirely free. As a 

 rule it joins the subcostal close to the base and runs contiguous with 

 it to the root. 



It is in the origin and character of vein 5 that the greatest and 

 most radical variation occurs, for we have within the limits of the 

 genus, as recognized here, perfect trifids, perfect quadrifids and very 

 good intermediids. There is even a very considerable range within 

 the limits of one species. The forms in which vein 5 is weak, aris- 

 ing from the cross-vein well removed from the median and not con- 

 nected with it by a strong spur, are sutrix, viegocnla, neocula, elerjan- 

 tula, cretata, behrii, virginalis, binocula, meskei, teuuicola, lihedis, 

 neomexicana, candefacta and erastroides. These are typical trifids. 



The species in which vein 5 is as fully developed as the others 

 and arises out of the median at the end of the cell, directly or on 

 a very short spur, are Jiauicoda, angustipennis, major, lanceolata, 

 gonella and areli. All these are true quadrifids, and, except areli, 

 all are narrow winged species. But not all narrow-winged species 

 are included ; and areli varies a little, tending to the third series, in 

 which vein 5 is little if any weaker than the others, and is from a 

 longer or shorter stout spur out of the median, and not from the 

 cross-vein. 



The species belonging to this third series are terminimaeulata, 

 deleeta, fiavipennis, abdominalis, lactipennis, expolita, sedata, nuicola, 

 lucasi, biplaga, quadriplaga, schwarzii, arida and coquillettii. All 

 these might be called intermediids. 



In one point nearly all these species agree ; they have veins 3 and 

 4 forked from the median at some distance beyond the cell. Expo- 

 lita, neocula and cretata are exceptions, 8 and 4 separating at the 

 end of the cell ; libedis is almost at the other extreme, the fork 

 occurring beyond the middle of the distance to the margin. The 

 venation therefore is as variable as it can well be within the family 

 limits. 



The scale covering of the upper surface is usually smooth and 

 glistening giving the insects a characteristic appearance. 



In the arrangement of the species several methods may be 

 adopted, based primarily upon the narrow, l)road or triangular 

 wing forms, upon the [)attern of maculation on the j)rimaries, 

 upon the color of tlie .secondaries, upon the structure of the front. 



