liyDROxArETRID^. 567 



Tliorax. — Pronotum ; the 1st 5th very concave, at the anterior 

 angles a small tubercle, the sides rounded, much incrassated ; the 

 middle with a short, longitudinal, yellow line in front ; sides, viewed 

 from beneath, from the anterior to the raised hinder angle with a 

 yellow line, widest posteriorly, interrupted at the constriction by a 

 black line coming obliquely from above, the anterior portion of the 

 yellow line on a higher level than the posterior part ; disk ; down the 

 middle, a somewhat strong keel, rather deepest on the scutellar 

 process. 'Elytra black, sometimes with pale spots between the 

 nerves ; nerves with golden scale-like hairs. Wings whitish, fuscous 

 posteriorly, iridescent. Stermim; JProsfernum depressed, yellow, 

 with a large quadrate, black spot in the middle not reaching quite to 

 the anterior margin ; Meso- and Metastermim very convex, black ; 

 Metasternum with a slight keel, but without a tubercle. Legs; 

 1st pair ; fulcra yellow, outwardly black ; thighs yellow-brown, paler 

 at the base ; on the upper \, above and beneath, a narrow, pointed, 

 black line ; tihicv brown, outwardly with a line, a spot at the apex, 

 and very short hair,«, black ; tarsi black : 2nd and 3rd pairs, sheath 

 of the coxro beneath, diagonally pale yellow on the posterior •!• ; 

 coxce and fulcra pale yellow ; thighs yellow-brown, paler at the base, 

 the sides with a brown line, the apex brown-black ; 2nd pair longer 

 than the 3rd ; tihice black, 2nd pair as long as the tibite and tarsi 

 together of the 3rd pair of legs ; tarsi black ; 2nd pair, the 1st joint 

 nearly 4 times longer than the 2nd ; 3rd pair, 1st joint 2:^- times 

 longer than the 2nd. 



Abdomen above, black, beneath with a slight middle keel, which 

 becomes obsolete posterioi-ly ; underside, in the (J black ; the Gth 

 segment posteriorly yellow, its posterior margin very concave, and 

 in the middle a deep round notch ; in the $ deep black at the sides, 

 the middle broadly yellow-brown, with a central, narrow black line 

 on the keel ; Connexivnm widened posteriorly, the margin with a 

 brown line. Genital segments above, black ; in the ^ the 1st 

 reaches much beyond the points of the connexivum, sides parallel, 

 posterior margin straight ; the 2nd short, narrow, the end rounded : 

 beneath yellow-brown, the 2nd slightly keeled posteriorly: in the 

 5 beneath, yellow-brown, the ] st flattened on the sides, and with 

 an oblique depression, the middle keeled at the base ; the 2nd short, 

 rounded. 



Length, 4 — 4-^ lines. 



Common on stagnant water from April to September, 



