146 HEMIPTERA-HETEROPTERA. 
the under surface and the lower portion of the pleura densely clothed with silvery pubescence, the 
pubescence on the pleura sometimes inclining to golden. Antenne rather stout, about reaching to 
the tip of the pronotum, joint 1 nearly or quite as long as 2 and 3 united, 2 and 3 subequal in length, 
4a little longer than 3. Pronotum with the short anterior lobe rounded at the sides and somewhat 
sharply demarcated from the posterior lobe; the latter rounded behind, flattened along the posterior 
margin, obsoletely carinate down the middle, and usually more or less transversely wrinkled. Elytra 
reaching as far as the tip of the last genital segment in the male, a little shorter in the female. Meso- 
pleura strongly and abruptly dilated before the laterally prominent intermediate coxe. Abdomen about 
as long as the thorax; the genital segments long in the male, much shorter in the female, the first 
segment much narrower than the terminal dorsal segment; the sixth connexival segment produced into 
a short spine at the outer apical angle in both sexes. Intermediate and hind legs very elongate. Anterior 
femora very stout and almost straight in the male, more slender in the female. Posterior tarsi with joint 
1 about two and one-half times longer than 2. Posterior femora a little shorter than the tibia and 
tarsus united. 
Apterous form. Pronotum covering the mesonotum, rounded at the tip, the two lobes subequal in width ; the 
posterior lobe varying in colour from obscure ferruginous to black, and usually transversely wrinkled. 
Mesopleura with a triangular silvery-pubescent patch behind. 
é. Ventral segments 3-6 rather broadly sulcate down the middle, the sixth also transversely depressed (its 
apical margin appearing raised), the apex of the latter broadly and deeply emarginate in the centre and 
also ciliate; first genital dorsal segment nearly as long as the preceding segment, slightly dilated at 
the sides posteriorly, the second segment shorter; first genital ventral segment longitudinally raised in 
the centre, the second segment long and subcordate. 
9. Ventral segments 3-6 faintly canaliculate down the centre, the sixth segment unemarginate at the apex. 
Two genital segments visible above, one beneath. 
Length 134-174, breadth (mesothorax) 33-44 millim. 
Hab. Nortn America, United States! ? 4, Texas, Colorado, Arizona, and Atlantic 
Region 3.—Mexico12 (Mus. Vind. Cws., ex coll. Signoret), Ciudad in Durango 8100 
feet (Forrer),'Omilteme in Guerrero 8000 feet (H. H. Smith); Guaremana, Quiché 
Mountains 7000 to 9000 feet ( Champion). 
This is the largest of the Central-American species of the genus, and it is apparently 
referable to G. remigis, Say, which is compared by its describer with G. paludum, Fabr. 
Numerous winged and apterous specimens of both sexes have been examined. The 
colour, as well as the sculpture, of the posterior portion of the pronotum is variable. 
The anterior femora are very stout. The male has the venter sulcate down the middle, 
with two large blackish spots on each segment, the sixth broadly and deeply emarginate 
at the apex. The female has the venter obsoletely canaliculate, with a dark stripe 
down the centre, divided by a pallid line. In the larger males the anterior femora are 
greatly incrassate. The following is a very closely allied form. 
2. Gerris robustus. 
Hygrotrechus robustus, Ubler, in Pickard’s Ins. salt water, Silliman’ s Journ. (3) i, p. 105 (e) 
(1871)*; Proc. Calif. Acad. Sci. (2) iv. p. 2887. 
Gerris aptera, Walk. Cat. Hemipt. Heteropt. viii. p. 165 (1873) °. 
Winged form. Closely allied to G. remigis, Say, and very similarly coloured, the posterior portion of the 
pronotum obscure ferruginous or ochraceo-ferruginous, the ventral segments without conspicuous blackish 
