1919] 



Hine: Genus Erax 107 



interruptus Macquart, Hist. Nat. I, 310, (Asilus), 1834. 



maculatus Macquart, Dipt. Exot., I, 2, 111, tab. IX, fig. 6, 1838. 



lateralis Macquart, Dipt. Exot., I, 2, IIG, 1838. 



ambiguus Macquart, Dipt. Exot., supl. 1, 84, 1846. 



villosus Bellardi, Saggio, II, 49, (Eristicus), 1861. 

 nemoralis Hine, Ohio Naturalist, XI, 311, 1911. 

 pallidulus Hine, Ohio Naturalist, XI, 309, 1911. 

 pilosus new species. 



planus Hine, Ohio Jr. Sci., XVII, 21, 1916. 

 rapax Osten Sacken, Biol. Centr. Am., Dipt., I, 201, 1887. 

 splendens Williston, Biol. Cent. Am., Dipt., I, 325, tab. VI, fig. 5, 1901. 

 stramineus Williston, Trans. Am. Ent. Soc, XII, 68, 1885. 

 texanus Banks, new species. 



triton Osten Sacken, Biol. Centr. Amer., Dipt., I, 200, 1887. 

 truncatus Hine, Ohio Naturalist, XI, 309, 1911. 

 varipes Willi.ston, Trans. Am. Ent. Soc., XII, 71, 1885. 



KEY TO GROUPS OF ERAX. 



1. Furcation of the third vein distinctly before the base of the second posterior 



cell making the second submarginal cell long 2 



Furcation of the third vein opposite or bevond the base of the second posterior 

 cell ' 4 



2. Three submarginal cells The anomalus group 



Two submarginal cells ' 3 



3. Rear of thorax and. scutellum with abundance of bristles, male abdominal 



segments six and seven silvery, female with tip of oviduct from above 



furcate The rufibarbis group 



Male abdomen usually with several segments silvery, female with tip of ovi- 

 duct from above never divided. Male, except in a very few cases, with 

 one or more abdominal segments bearing long white hair parted at the 

 middle and directed outward The stramineus group 



4. Posterior branch of the third vein curved backward at tip, meeting the costa 



at or beyond the apex of the wing The aestuans group 



Posterior branch of the third vein curved forward, meeting the costa plainly 

 before the apex of the wing 5 



5. Mesothorax compressed anteriorly and with a conspicuous crest of erect 



hairs on the mid-dorsal line The carinatus group 



Mesothorax broadly rounded above and without a conspicuous crest of hairs. .6 



6. Mesothorax with numerous bristly hairs which are unusually long, scutellum 



conspicuously hairy and with numerous marginal bristles. .The aridus group 



Mesothorax with very short hair anteriorly, a few rather prominent bristles 



posteriorly. Scutellum with short hair on the disc and usually with not 



more than half a dozen bristles on its margin 7 



7. Male with ventral prominences on abdominal segments four, five and six, 



small slender species The tuberculatus group 



Male abdomen without ventral prominences usually large or medium sized, 

 robust species The barbatus group 



