46 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
As indicated above, the variation in color of the mesonotum 1s 
considerable, so that the characters overlap on all sides, and speci- 
mens occur which cannot be correctly placed with any table. The 
male genitalia are necessary for determination in such cases, espe- 
cially in the subgenus eteronycha, where the confusion due to this 
variability is likely to be greatest. 
KEY TO THM UNITED STATES SPECIES OF HETERONYCHA BY THE MALE GENITALIA. 
1. Basal lobes modified, obsolete as such, but leaving a large spine on one side 
and two approximate setae on the other, the latter sometimes obsolete. 
(Group Pullatus) 2. 
Basal lobessmoresor lessidevelopedi == a 4, 
2. Basal tobe larceswith=twouSlout Spineshan ae 3. 
Basal lobe small, with two stout spines___--______-__---- pullatus Coquillett. 
Basal lobevabsentno basal spines2=222 25" 4 eee aurifer Coquillett. 
3; Acslight hairy area distallof® apical lobeies="ss22——+— =e intrudens Dyar, 
A strong hairy area proximal of apical lobe. 
diantaeus Howard, Dyar, and Knab. 
4, Basal lobe elongate, semidetached, the setiferous part separate from the 
SPEC esta me hbase Sere! BP iee ERS eo (Group Serratus) 5. 
Basal lobe sessile, the setae not apart from the spine, or spine wanting__ 8. 
5. Basal lobe of side piece rounded and bulbous_—_______ 6. 
This*lobesvelongvateds fingers shaped) stesu hess a eee Ue 
6. Filament of claspette broadly bladeshaped___----_- bimaculatus Coquillett. 
Kilament of ‘claspette slender2 222. 232222 see dupreei Coquillett. 
7. Stem of claspette thick, sinuous____--_-_----_--~_- atlanticus Dyar and Knab, 
Stem of claspette slender, less sinuous__--~-_----_ tormentor Dyar and Knab. 
8. Basal lobe more or less expanded and tubercular, with or without a 
SPU SiS a eed seedy eer =e a Ee etn bt Rea Bath ak 2 ees a ech 9 
Basal lobe unitormly, long-haired, no spine=—22s2 2 Seon eee Dike 
9. Basal lobe expanded, with many setae, but without a single differentiated 
long spine; if the marginal spines are thickened, more than one is in- 
VOU Wi OEE at as page ees ae ke (Group Dorsalis) 10. 
Basal lobe with a single differentiated spine, or if absent, the lobe if flat 
EDT OLE TE USE OS I a Sa re alal 
10. Basal lobe without spines on the margin____--_______ canadensis Theobald, 
Basal lobe with coarse spinelike setae on the margin. 
campestris Dyar and Knab, 
Basal lobe with two stout spines on the margin--__----~---- dorsalis Meigen. 
11. Apical lobe with short flat clinging setae________--__- (Group Punetor) 12. 
Apical lobe with the setae normal or slightly thickened__________--_-_-_ alas 
124 Spinetot *basallobesai normalispine = + asama ieee eee 13 
spencerii Theobald. 
idahoensis Theobald. 
This spine greatly thickened and delicate____-__-_- hirsuteron Theobald. 
aestivalis Dyar. 
aldrichi Dyar and Knab. 
dysanor Dyar. 
punctodes Dyar. 
Claspettet filament short: cu rye dee ee 14. 
13. Claspette filament long, sickle shaped____________-_______. 
