the shape of individual eggs being long and cylin- 

 drical. Egg parasites, Patasson gerrisophaga (Doutt), 

 have been reared from Gerris in California. Hungorford 

 found that the incubation period for G. remigis was 

 two weeks in Kansas. There were five instars, each 

 lasting about one week. 



Distribution. —Most of our Gerris species are widely 

 distributed. G. remigis occurs throughout North Amer- 

 ica and marginatus is nearly as widespread. Nyctalis 

 is very closely related to remigis and has not been 

 recognized with certainty from California since 1928 

 when Drake and Harris reported it from Fresno. The 

 other large species, notabilis, was formerly considered 

 to be the Holarctic Limnoporus rufoscutellatus, but 

 the latter is now regarded as distinct, occurring in 

 Europe and in Alaska, and two other North American 

 species are recognized, dissortis in the East and 

 notabilis in the West. The remaining species of Gerris 

 are all small and all northern in distribution. 



Metrobates is strictly an American genus with its 

 center of distribution in the tropics. Although wide- 

 spread and common in the eastern United States it 

 has been only recently recorded from California 

 (Usinger, 1953). The northern California form (M. trux 

 infuscatus Usinger) is darker than typical M. trux of 

 the southwestern United States and the Colorado 

 River region of southern California. 



Trepobates is also a tropical American genus which 

 is widespread in the eastern United States but is here 

 recorded for the first time from the southern border 

 of California at the Colorado River. 



Halobates is tropicopolitan, occurring in the open 

 ocean and in protected reefs of tropical islands. 

 H. sericeus has been taken in the warm (16.22° C) 

 waters about two hundred miles off the Monterey 

 Coast (34° 54.5 N latitude; 124° 29 W longitude) 

 (H. R. Attebery, Scripps Inst. Oceanography, in litt.) 



Taxonomic characters. — The most distinctive char- 

 acters of gerrid species are the male genitalia. 

 Fortunately the apical connexival spines of females 

 are also distinctive in many instances, although the 

 latter vary to some extent with wing polymorphism. 



Key to Genera of Gerridae 



1. Inner margins of eyes sinuate or concave behind the 

 middle, body comparatively long and narrow. Gerrinae 



2 



— Inner margins of eyes convexly rounded; body compar- 

 atively short and broad. Halobatinae 3 



2. Pronotum sericeous, dull; basal segment of front tarsi 

 but little shorter than apical segment (fig. 7:24); wide- 

 spread Gerris Fabr. 1794 



— Pronotum glabrous, shining; basal segment of front 

 tarsi much shorter than apical segment; eastern and 

 southern United States and tropicopolitan 



Limnogonus Stal 1868 



3. Tibia and first tarsal segment of middle leg with a 

 fringe of long hairs; always apterous, the meso- and 

 metanota fused, without trace of a dividing suture 

 (fig. 7:26); marine; widely distributed 



Halobates Esch. 1822 



— Tibia and first tarsal segment of middle leg without a 

 fringe of long hairs; dimorphic, the meso- and metanota 

 of apterous forms with a distinct dividing suture situ- 

 ated at the bases of the posterior (dorsal) acetabula 



4 



213 



Usinger: Hemiptero 



First antennal segment subequiil to the remaining; '•', 

 together; body relatively short, broad and subf lattcrn-'l, 

 about half as wide as long from olypeua to apex of 

 abdomen (fig. 7:256); swift-flowing streams; widely 

 distributed in the Western Hemisphere 



Metrobates Uhl. 1878 



First antennal segment much shorter than the remaining 

 3 together; body relatively longer and narrower and 



more convex, about 1/3 as wide as long 5 



Third antennal segment with several stiff bristles; 

 males often with strikingly incrassate or curved anten- 

 nae and hind femora; eastern and southern United States 



Rheumatobates Bergr. 1892 



Third antennal segment with fine pubescence only; 

 male antennae and femora not modified (fig. 7:25a); 

 eastern and southern United States to southern Cali- 

 fornia Trepobates Uhler 1894 



r\ r 



Fig. 7:26. Halobates sericeus Esch., male, Kailua, Oahu, T. H. 

 (V. Fosberg) (Zimmerman, 1948). 



