202 



Usinger: Hemiprera 



flowing from hot springs in the Amargosa River system 

 in southern Nevada and Death Valley, California. The 

 characteristics of the water are as follows (La Rivers, 

 1953): temperature 32.2°C (90°F); pH— 7.3; C0 2 — 20 

 ppm.; C0 3 — lacking; HC0 3 — 256 ppm; DO— 2.7 ppm. 

 Taxonomic characters.— Aside from size, color, and 

 contour, which are distinctive for each species but 

 difficult to delimit, the chief distinguishing characters 

 of naucorids are the form and extent of the propleura 

 and the genital process of the male and genital plate 

 of the female (fig. 7:15). The male genital segments 

 move as a unit and are fixed to the basal abdominal 

 segments only at the middle. In mating they are bent 

 downward and turned slightly to expose a prominent 

 hook (absent in A. funebris and amargosus) on the 

 caudal margin of the fifth tergite on the right side. 

 This process is very distinctive in size and shape 

 for each species and may be examined by softening 

 the specimen and bending the genital segments down- 

 ward. The female subgenital plate is the large median 

 plate at the apex of the ventral surface of the ab- 

 domen. The form of the apical margin of this plate is 

 distinctive for our species. 



Key to Nearctic Genera of Naucoridae 

 Adults 



1. Anterior margin of pronotum straight or scarcely con- 

 cave behind interocular space 2 



— Anterior margin of pronotum deeply concave behind 

 interocular space 3 



2. Inner margins of eyes anteriorly divergent; meso- and 

 metasterna bearing prominent longitudinal carinae which 

 are broad and foveate along middle; body broadly oval, 

 subf lattened, the embolium produced outward and 

 backward as an acute spine. Limnocorinae (fig. 7:13) 



Usingerina La Rivers 1950 



— Inner margins of eyes anteriorly convergent; meso- and 

 metasterna without longitudinal carinae at middle; 

 body strongly convex above, the embolium rounded. 

 Naucorinae (fig. 7:14) Pelocoris Stal 1876 



3. Prosternum completely exposed, separated from the 

 flattened pleura by simple sutures; abdominal venter 

 naked and with a disclike area near each spiracle; 

 dimorphic, the brachypterous forms with hemelytra 

 truncate at apices, about half as long as abdomen. 

 Cryphocricinae Cryphocricos Signoret 1850 



— Propleura produced platelike over posterior part of 

 prosternum, subcontiguous at middle and completely 

 covering this part of prosternum; abdominal venter 

 densely pubescent, interrupted by small holes at 

 spiracular openings and by a transverse row of small 

 holes behind each spiracle; macropterous (fig. 7:12) 

 Ambrysinae Ambrysus Stal 1862 



Last Instar Nymphs 



1. Abdominal venter naked; front femora long and slender, 

 with 1 ventral and 2 posterior longitudinal ridges of 

 granules Cryphocricos Signoret 1850 



— Abdominal venter pubescent; front femora roundly in- 

 flated, without ventral and posterior longitudinal 

 ridges 2 



2. Inner margins of eyes anteriorly divergent; mesosternum 

 bearing a longitudinal carina which is foveate along 

 the middle Usingerina La Rivers 1950 



— Inner margins of eyes convergent anteriorly and also 

 to a certain extent posteriorly; mesosternum without 

 a foveate carina 3 



3. Anterior margin of pronotum scarcely concave behind 



interocular space Pelocoris Stal 187G 



— Anterior margin of pronotum deeply concave behind 

 interocular space Ambrysus Stal 1862 



Usingerina moapensis La Rivers 1950 (fig. 7:13) is 

 known only from Warm Springs, Clark County, Nevada, 

 where it was taken in the gravel bed of a stream. 

 The temperature of the water was 75° to 89° F. 



Pelocoris shoshone La Rivers 1948 (fig. 7:14) is 

 known from the White River system in southeastern 

 Nevada and from the Amargosa River system in Nevada 

 and Death Valley, California (La Rivers, 1953). Two 

 nymphs in the collection of the University of Kansas 

 bear the label, "Nipomo, Santa Barbara County, 

 California." 



Key to the California Species of Ambrysus 

 Adults 



1. Connexival margins of first and second visible seg- 

 ments smooth, those of segments 3-5 minutely serrate 

 (best seen from below); size small, 6-6.5 mm. (fig. 

 7:156); Hot Springs, Ash Meadows, Nye County, Nevada 



amargosus La Rivers 1953 



— Connexival margins smooth; size usually larger ... 2 



2. Propleura not contiguous, separated by a small but 

 distinct gap at middle over prosternum; hemelytra 

 greenish- or yellowish-brown with ill-defined paler 

 markings at base of embolium. calif ornicus subspp. 



3 



— Propleura contiguous over middle of prosternum; 

 hemelytra black with distinct pale markings at least 

 at base of embolium and usually at inner apex of 

 embolium and at middle of apical margin of corium 



4 



3. Connexival angles produced into small but distinct 



Fig. 7:14. Pelocoris shoshone La Rivers, female, Warm Springs, 

 Clark County, Nevada, December 26-27, 1948 (La Rivers). 



