246 TERTIARY INSECTS OF NORTH AMERICA. 



broad. The first oblique vein is straight and parts from the postcostal at 

 scarcely more than forty five degre.es, and the second oblique, which is also 

 straight, at as little less, the first discoidal cell being, nevertheless, only 

 moderately long and narrow, and more than three times as broad on the hind 

 margin as at base. Cubital vein broadly arcuate, occupying the middle 

 of the space assigned to it, first forking at scarcely more than a third way 

 to the hind margin and again at less than half-way to the tip. Stigmatic 

 vein parting very narrowly from the stigma, so that the stigmatic cell is very 

 slender and nearly or quite a third the length of the wing. 



Length of body, 4 mm ; of fore wing, 6 mm . 



Named for Dr. Charles Valentine Riley, whose researches on the grape 

 root aphid, Phylloxera, to mention only this, are widely known. 



Florissant. One specimen, No. 2916. 



2 ARCHILACHNUS Buckton. 



ArcMacknus Buckt., Monogr. Brit. Aphides, IV, 177 (1883). 



The head appears to be without frontal tubercles, and the antennae are 

 slender, almost as long as the body (perhaps longer), with the basal joints 

 as in Aphis. Fore wings with the stigniatic vein arising from the middle of 

 the stigma. Cubital vein twice forked, the first time at a moderate distance 

 from its origin, which is near the middle of the proximal half of the space 

 between the base of the first oblique and stigniatic veins, the second time 

 as far beyond the origin of the stigniatic as it is beyond the first fork of the 

 cubital vein. Second oblique vein arising a little nearer the first oblique 

 than the cubital vein, at an angle of about forty -five degrees with the post- 

 costal, the first at a distinctly less angle, so that the first discoidal cell 

 between them i.s about six times as broad on the hind margin as at the 

 base. Legs moderately stout, the hind pair about as long as the fore 

 wings. Abdomen broad ovate with a short and moderately stout cauda. 



The genus was not separately characterized by Buckton. I do not see 

 any special relation to Lachnus. 



Table of the species of ArohVachnus. 



Large and stout species. Ciiliitnl vein l>rni ;it its first furcation, otherwise str.liglit. . .1. A. pcniiatus. 

 Small and sleuder Hpecios. Cubital veiu gently aicuato throughout tho lirst two-thirds of its course. 



2. A. mudyei. 



