271 ) 
N'OKTH AMERICAN GYRINUS (cOLEOPTERA) 
Spocios of medium size, average length about d.o mm., rarcdy less than 
■) mm., reflexed lateral margins wider (1 
Speeies of small size, average length about 4.5 mm., rarely as great as 
5 mm., rcflexed lateral margins very narrow 7 
(i. A|)(>x of middle lobe of eodeagus truncate with a slight ])rojecting angle 
at middle, lateral angles distinct 3. venlralin 
Apex of middle lobe of eodeagus broadly angulate at middle, lateral 
angles rounded 4. f rater inis 
7. Surface distinctly and nearly uniformly bronze<l, form moderately con- 
vex 5. aeiieolafi 
Surface not or only feebly bronzed, form more strongly convex S 
8. Surface feebly bronzed, female extremely finely alutaceous; middle lobe 
of oedeagus about one-half as wide ai)ically as the lateral lobes. 
6. woodruffi 
Surface not bronzed, female not detectably alutaceous; middle lobe of 
o(‘deagus distinctly wider a[)ically than the lateral lobes. 7. margincllus 
9. Size small, average length less than 4.5 mm 10 
Size larger, average length greater than 5 mm. (except elevalus) 11 
10. Transverse jn^jiiotal impressed line of ))unctures parallel with and rather 
close to the front margin; venter brownish piceous except at apex. 
S. dichrnm 
'rran.sverse jn’onotal line of punctures more arcuate laterally and there- 
fore more distant from the front margin; color beneath nearly uni- 
form 9. latiliinhiis 
11. Sui’face finely alutaceous and minutely punctulate, more noticeably so 
in the female 12 
Surface highly polished, and either not at all alutaceous or punctulate, 
or only visibly so under high power 13 
12. Upper surface, except margins, scarceU bronzed; average length a little 
less than (i mm.; middle lobe of oetleagus constricted at apical third. 
10. hifariiis 
Ui)per surface more or less bronzed; average length rather greater than 
(3 mm.; middle lobe of oedeagus without constriction.. 11. coiifuiis 
13. (.'olor beneath nearly uniform, surface without trace of micro-sculpture 
in either sex 14 
Color beneath normall}^ darker medially than along the margins. ... Hi 
M. Elytra with a short elevated plica at the outer apical angle. 12. plicifer 
Jdylra without plica at apical angle 15 
15. J'’orm broad and strongly convex, average length approaching ti mm. 
13. parhi/tioniii.'i 
I'oi'm narrow, longit udinal jn'otile st rongly (!onv('x and (list imd ly gibbous; 
size mmdi smalh'r, average length ratlua- less than 5 mm. I I. eleralas 
