562 HYDROMETRINA. 



uexivum ; the 2iid short, triaugular ; beneath, the 1st long, its pos- 

 terior margin sinuate, lengthened on the sides ; the 2nd lies within 

 the 1st, deflected, its posterior margin broadly rounded ; the 3rd as 

 on the upperside: in the ? above, the 1st segment, reversed 

 trapeziform, does not reach to the points of the connexivum ; the 

 2ud, narrow, obconic, is longer than the 1st, and projects much 

 beyond the points of the connexivum; beneath, the 1st gradually 

 narrowed posteriorly, its posterior margin rounded, the sides com- 

 pressed into a hollow towards the base, but at the basal angles pro- 

 minent ; the 2nd as on the upper side. 



Length, c? 6 ; ? 7^ lines. 



In winged examples the pronotum is somewhat widened to the 

 hinder angles, which are raised into a small rounded tubercle, and 

 the scutellar process is more produced ; the Elytra are dark brown 

 or black, sometimes as long as the abdomen, sometimes abbreviated ; 

 the nerves strong, brown, with golden hairs ; the Wmgs whitish, with 

 a fuscous shade, iridescent ; in other respects the winged are like the 

 apterous specimens. 



The apterous form is common on streams from April to October, 

 where the insects run with rapidity against the current ; but among 

 hundreds of examples taken at different periods of the summer, we 

 never found one with wings. But Mr. Dale once took 3 pairs 

 winged in his own pond, where the water is nearly stagnant ; into 

 this pond, a few days previously, he had put 3 pairs of apterous 

 specimens taken from a stream ; and although he cannot prove they 

 were the same that he afterwards caught, he believes they were, as 

 he never found the species in his pond before or since. 



Species 3. — Hydrometra thoracica. 



Geeeis ttiokacica, Schum. Beitr. 2, 46, 8 (1832) ; //. Schf. Nom. Ent. 

 63 (1835). 

 — RUi'OSCUTELLATA, Curt. B. E. xij, 553, 3 (1835). 

 Hydeometka thoeacica, H. Schf. Watiz. is, 67 & 71, t. 301, fig. 9 28 

 (1850) ; Flor, Rbyn. Liv. i, 739, 5 (ISGO)} 

 Fielj. Eui-op. Hem. 108, 6 (1861). 



Above black-brown; i\\e pronotum in the middle of the hinder J-, ■ 

 broadly reddish or yellowish-brown, the undercurved side 

 margins yellow from the constriction to the hinder angles. 



