203 

 Usinger: Hemiptera 



Head broader, more than 1/2 again a.s wide across 



eyes as long (57:35) (fig. 7:12) mormon Montandon 



Pronotum relatively narrow, \* A times as wide as head; 



pronotum distinctly spotted laterally 



funebris La Rivera 



Pronotum broader, 1^ as wide as head, the lateral areas 

 unspotted calif ornicus Mont andon 



Fig. 7:15. Ambrysus genital segments, the top outline in each 

 case representing the hind margin of the female subgenital plate, 

 and the outline beneath it the dorsal process of the hind margin 

 of the fifth visible tergite in the male, a, Ambrysus occidenfalis 

 La Rivers; b, A. amargosus La Rivers; c, A. funebris La Rivers; 

 d, A. puncficol lis Stal; e. A, mormon Montandon; f, A. cali- 

 {ornicus Montandon. 



spines; northern California; streams in the coast 

 Ranges bohartorum Usinger 1946 



— Connexival angles scarcely produced, little more than 

 right angles (fig. 7:15/); southern California 



calif ornicus Montandon 1897 



4. Size small, 6-6J^ mm.; no dorsal genital process in the 

 male (fig. 7:15c); Death Valley, stream from a hot 

 spring, 36° C funebris La Rivers 1949 



— Size larger, 8-15J2 mm.; genital process of fifth ab- 

 dominal tergite of male well developed 5 



5. Corium unspotted, unicolorous; size large, 13 mm. or 

 more; female genital plate unisinuate (simply, shallowly 

 concave) at apex (fig. 7:15rf); stream near Parker Dam, 

 Colorado River puncticollis Stal 1876 



— Corium variously marked with pale areas; size smaller, 

 8-12' /2 mm.; female genital plate trisinuate at apex 



6 



6. Head more than half as wide, eyes included, as greatest 

 width of pronotum, in ratio of 7:13, corium with a large 

 bilobed spot at inner apex of embolium and a large 

 crescent-shaped spot at middle of apical margin; male 

 genital process as broad as long; female genital plate 

 only feebly concave at middle of apex (fig. 7:15a); 

 southern California streams 



occidentalis La Rivers 195 1 



— Head slightly less than 1/2 as wide as pronotum; 

 corium with a small spot at inner apex of embolium 

 and at middle of apical margin or rarely without spots 

 (fig. 7:12); male genital process much longer than 

 wide; female genital plate deeply concave at middle 

 of apex (fig. 7:15e); northern and central California, 

 streams and shallow margins of lakes 



mormon Montandon 1909 



Key to Last Instar Nymphs of Ambrysus 



Lateral margins of abdominal segments entire, smooth; 

 size large, 12 mm.; color rather uniform dark brown on 



meso- and metanota and abdomen puncticollis Stal 



Lateral margins of abdominal segments minutely but 

 distinctly serrate or crenulate; size less than 10 mm.; 

 ground color ochraceous with a regular pattern of brown 



markings on thorax and abdomen 2 



Head approximately 1/2 as wide across eyes as great- 

 est width of pronotum (0.49 to 0.52) 3 



Head much more than 1/2 as wide across eyes as 



greatest width of pronotum 4 



Head relatively small, 1/2 again as wide across eyes 

 as long (51:35) occidentalis La Rivers 



REFERENCES 



LA RP/ERS, IRA 



1948. A new species of Pelocoris from Nevada, with 

 notes on the genus in the United States. Ann. Knt. 

 Soc. Amer., 41:371-376. 



1950. A new Naucorid genus and species from Nevada. 

 Ann. Ent. Soc. Amer., 43:368-373. 



1951. A revision of the genus Ambrysus in the United 

 States. Univ. Calif. Publ. Entom., 8:277-338. 



1953. New Gelastocorid and Naucorid records and 

 miscellaneous notes, with a description of the new 

 species, Ambrysus amargosus. Wasmann Jour. Biol., 

 11:83-96. 

 THORPE, VV. II. 



1950. Plastron respiration in aquatic insects. Biol. Rev., 

 25:344-390. 

 USINGER, R. L. 



1941. Key to the subfamilies of Naucoridae with a generic 

 synopsis of the new subfamily Ambrysinae. Ann. Ent. 

 Soc. Amer., 34:5-16. 



1946. Notes and descriptions of Ambrysus Stal, with an 

 account of the life history of Ambrysus mormon Montd. 

 Univ. Kansas Sci. Bull., 31:185-210. 



1947. Classification of the Cryphocricinae. Ann. Ent. 

 Soc. Amer., 40:329-343. 



Family BELOSTOMATIDAE 



Giant Water Bugs 



Giant water bugs have attracted the attention of 

 naturalists in America for more than one hundred 

 years by their large size, their habit of flying to 

 lights, and the curious characteristic exhibited by 

 some genera of laying eggs on the backs of the males. 

 Other common names are "fish killers," "electric- 

 light bugs" and "toe-biters." Belostomatids are 

 large, dorsally subflattened, brown bugs with the 

 rostrum short and stout, antennae concealed in ven- 

 tral grooves behind the eyes, front legs raptorial, 

 and apex of abdomen with a pair of short, straplike, 

 retractile appendages. The hind legs are flattened 

 and ciliated for swimming. The tarsi, in the adults 

 of our species, are two-segmented with one claw on 

 the front legs and two claws on the middle and hind 

 legs. The tarsi are one-segmented in the nymphs, 

 and there are two prominent claws on the middle and 

 hind tarsi of nymphs and two equally developed claws 

 on the front tarsi of nymphs of Lethocerus and Bena- 

 cus. The outer claw of the front tarsus of Belostoma 

 and Abedus nymphs, on the other hand, is reduced 

 and is totally absent in later instars (Bueno, 1906). 

 Students of animal behavior have studied the curious 

 "death-feigning" habit which is reported for Belo- 

 stoma and Abedus. When disturbed by removal from 

 water or by contact with the dorsal and ventral sur- 

 faces of the body, the bugs assume a characteristic 

 rigid position and remain in this so-called "death- 



