198 BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



Face et front jauues, a duvet blanchatre et bande noire; style des 

 antennes brun. Cotes du thorax noirs ; dcussou brun. Les bandes de 

 I'abdomen 6troites ; celles des premier et deuxieme segments 6largies et 

 faiives siir les c6t(?s: ventre noir, a incisions blancbatres. Jambes in- 

 terniediaires fauves, a extr^mite brunatre. Ailes assez claires ; pre- 

 miere nervure trausversale sita^e an -dela de la moitie de la cellule dis- 

 (toidale. 



ADDITIONAL NORTH AMERICAN SPECIES. 



Helophilus formalis [femoralis'] Walker, List, etc., iii, 603. — Mexico. 



Helophilus Androclus Osten Sacken, Cat. Dipt., 250, note 230: Walker, List, etc., 

 iii. G12 (EristaUs). — British Possessions. 



Helophilus f rater Osten Sacken, Cat. Dipt., 250, note 230; Walker, List, etc., iii, 

 613 (Eristalis). — Hudson's Bay Territory. 



Helophiluii chalepus Osten Sacken, Cat. Dipt., 250, note 230; Walker, Dipt. Sannd., 

 247 (Eristalis). — Canada. 



Baron Osten Sacken Irom an examination of the types of these 

 species, described as £Jmfrt7/.9, ascertained that they belong to the group 

 of H. borealis, (jroenlandieus, and glacialis. Thej' cannot be recognized 

 from the descriptions. 



PTERALLASTES. 



Pterallasies Loew, Centur., iv, 80, 1863. 



Head broader than the thorax, much flattened. Eyes bare, broadly 

 contiguous in the male. Frontal triangle small, antennal i)rominence 

 short, obtuse. Antennae inserted rather below the middle of the head 

 in profile, rather small; first two joints short, third joint rounded; 

 arista basal, bare. Face in the male nearly perpendicular, not descend- 

 ing far below the eyes, in profile gently concave above and more gently 

 convex below, arched, not carinate ; in the female concave ; obliquely 

 truncate below ; cheeks narrow, the lower border forming with the plane 

 of the occiput a little niore than a right angle. Scutellum wholly yel- 

 lowish opaque like the dorsum of the thorax. Abdomen elongate oval, 

 nearly twice as long and broader than the thorax, broadest at tip of 

 second segment, thence gently narrowed to the tip of the fourth. Legs 

 wholly unarmed, rather stout; hind femora moderately thickened, elon- 

 gate, below with short bristly hairs; hind tibije considerably arcuate, 

 flattened. Marginal cell of wing open, third vein with a deep sinuosity 

 into the first posterior cell; anterior cross-vein very oblique, near outer 

 third of discal cell, last section of fourth vein strongly sinuate, terminat- 

 ing near the tip of third vein ; sixth vein nearly straight. 



Large, rather thickly ])ilose, moderately elongate species. Thorax 

 densely yellowish pollinose ; abdomen black, shining. Type of genus, 

 P. thoraclcuH Loew, North America. ^ 



•Pterallastes thoracicus. (Plate VIII, figs. 9, 9a.) 

 PteraUasfes thoracicus Loew, Centur., iv, 80. 

 Habitat. — Pennsylvania! 

 3 . Length, to 12.5'"'". Face black, rather thickly covered with gray- 



