Casey — A Revision of the American Paederini. 191 



LathroUuin. The genera known to me by actual examples 

 may be defined as follows : — 



Neck moderately narrow, varying from a fourth to nearly a third as wide as 



the head 2 



Neck extremely slender 4 



2 — Gular sutures parallel, broadly, feebly arcuate, moderately separated 



throughout but most approximate at the middle; labrum broadly trun- 

 cate with the usual rounded median notch, bidentate or edentate; body 

 parallel, moderately convex, always pale in color, the anterior thoracic 

 angles distinct and subapical; tarsi moderately short, the posterior 

 slender with the two basal joints subequal. Rocky Mountain regions. 



Leucorus 

 Gular sutures more or less widely separated, more arcuate and most ap- 

 proximate anteriorly, diverging thence gradually to the base; labrum 

 distinctly quadridentate ; hind tarsi short, moderately slender, with the 

 basal joint but little longer than the second; body black or blackish, 

 polished and more or less sparsely punctate 3 



3 — Body thick and more convex, the legs thicker, the anterior tarsi di- 



lated; thoracic angles broadly rounded and almost obliterated, the 

 prothorax oval; labrum truncate ; gular sutures distinct. Entire United 



States except the true Pacific coast fauna Pycnorus 



Body slender, moderately convex, the legs slender; anterior tarsi not dilated 

 though broader and thickened; prothorax oblong, the anterior angles 

 more or less distinct; labrum rounded; gular sutures very feeble, 

 sometimes nearly obliterated . Entire Pacific coast region Orus 



4 — Posterior tarsi rather short, moderately thick, with the basal joint never 



more than slightly longer than the second, the anterior very feebly 

 dilated; labrum rounded in outline, distinctly quadridentate, the teeth 



simple ; body slender, parallel and moderately convex 5 



Posterior tarsi long, very slender, with the basal joint always distinctly 

 longer than the second, the anterior not or very feebly dilated; body 

 subparallel, strongly convex, the prothorax oval with the anterior angles 

 obtuse or subobliterated and far from the apex 6 



5 — Body minute in size, variable in color, more or less alutaceous because 



of minute dense punctuation; prothorax suboblong, with the anterior 

 angles more or less distinct ; gular sutures moderately widely separated, 

 most approximate anteriorly, gradually diverging thence to the base. 



Europe and America. [= Leptorus Csy .'\ Scopaens 



Body larger, black, polished, the punctuation less fine and rather sparse; 

 prothorax oval, the anterior angles obliterated; gular sutures parallel, 

 nearly straight, rather approximate throughout the length of the head. 

 Entire northern United States Scopaeoiua 



6 — Body very minutely punctulate and pubescent; labrum broadly rounded, 



large, very coarsely quadridentate and deeply cleft at the middle, the 

 inner teeth each with an internal denticle at base, or, unequally bifid; 

 gular sutures virtually coalescentfrom a short distance behind the sup- 

 port of the mentum. Eastern United States Scopaeopsis 



Body polished, subglabrous and subimpunctate, with sparse erect tactile 

 setae; labrum broadly rounded, with the usual small median emargi- 



