presumably primitive, has well-developed ocelli, and 

 Diaprepocoris, Micronecta, and Tenagobia have the 

 scutellum exposed. All other corixids have the scutel- 

 lum almost or entirely covered by the pronotum. 



Taxonomic characters. — The taxonomy of the Corix- 

 idae has long been based on the chaetotaxy of the 

 highly specialized front tarsi (palae) of the males. 

 The position and arrangement of the pegs in the so- 

 called peg row are characteristic for the members of 

 each genus and are usually distinctive for each 

 species. Therefore diagrams are given of the palae of 

 the California species (fig. 7:9). 



The male genital characters are also definitive in 

 most cases. The abdominal segments are asymmetri- 

 cal, and this asymmetry may be dextral (the genitalia 

 directed toward the right) or sinistral. This proves 

 to be a very conservative and useful character, con- 

 sistent for all the species in a given genus (at least 

 in our fauna). However, curious cases of reversed 

 symmetry have been recorded. For example, Hunger- 

 ford (1948) reports two sinistral specimens in a series 

 of six hundred males of Hesperocorixa laevigata (Uhl.). 

 A so-called strigil (which apparently has nothing to 

 do with stridulation) is located on the sixth abdominal 

 tergite in all our genera but Callicorixa. It is made up 

 of rows of comblike teeth and is said to grip against 

 the female venter in copulation. It is on the left side 

 in sinistral asymmetry and on the right side in dextral 

 species. 



Characters of the internal genitalia are easy to 

 observe if the tip of the abdomen is softened and the 

 capsule is teased out with a needle. The shape of the 

 right clasper is usually distinctive for each species. 



Simplified Key to Nearctic Genera of Corixidae 

 Based largely on characters of males 



1. Rostrum without transverse sulcations. Cymatiinae; 

 Ilolarctic, northern North America . . .Cymatia Flor 1860 



— Rostrum with distinct transverse sulcations. Corixinae 



2 



2. Eyes protuberant with inner anterior angles broadly 

 rounded. Glaenocorisini 3 



— Eyes not protuberant and inner angles normal 4 



3. Male pala dorsally expanded at base; northern Canada, 

 Europe Glaenocorisa Thomson 1869 



— Male pala not dorsally expanded at base; northern North 

 America Dasycorixa Hungerford 1948 



4. Palae similar in both sexes, peg row adjacent to upper 

 palmar bristles. Graptocorixini 5 



— Palae dissimilar, males with peg row separated from ■ 

 upper palmar bristles. Corixini 6 



5. Male abdomen sinistral. Strigil absent; southwestern 

 United States, Mexico ■ Neocorixa Hungerford 1925 



— Male abdomen dextral. Strigil present; western United 

 States, Central America .. Graptocorixa Hungerford 1930 



6. Male abdomen sinistral; North, Central, and South 

 America Trichocorixa Kirkaldy 1908 



— Male abdomen dextral 7 



7. Strigil absent 8 



— Strigil present 10 



8. One row of pegs above upper palmar bristles; south- 

 western United States, Mexico 



Morphocorixa Jaczewski 1931 



— Two rows of pegs above upper palmar bristles 9 



9. Front tibiae triangularly produced and flattened apically; 

 Sonoran, Neotropical Centrocorisa Lundblad 1928 



— Front tibiae not triangularly produced and flattened 



191 



Usinger: Hemiptera 



apically; northern North America 



Callioorixa White is7.'i 



10. Vertex of male with a distinoi longitudinal i 



anteriorly; pala ■ i i • • ■ [ . I \ i in|>n saed dorsally; <-a. M-m and 



southern United States; Mexico 



Itamphocorixa Abbott 1912 



Vertex of male not carinate; pala not deeply impressed 

 dorsally 11 



11. Seventh abdominal tergite with a small dextral hook; 

 eastern North America Palmacorixa Abbott 1912 



— Seventh abdominal tergite without a dextral hook .... 12 



12. Pala with 2 rows of pegs, one in row of upper palmar 

 bristles; southwestern United States to Guatemala 



Pseudocorixa Jaczewski 193 1 



— Pala without a row of pegs in upper palmar bristles 



13 



13. Pala with 2 distinct rows of pegs above upper palmar 

 bristles (fig. 7:9e-A); United States and Mexico 



Corisella Lundblad 1928 



— Pala with 1 variously curved, sinuate, or interrupted 

 row of pegs 14 



14. Prothoracic lobe quadrate or trapezoidal; Ilolarctic, 

 northern North America ... .Hesperocorixa Kirkaldy 1908 



— Prothoracic lobe narrdwer than long 15 



15. Hemelytral pattern not reticulate; hemolytra and face 

 not hairy (fig. 7:5a); cosmopolitan 



Sigara Fabricius 1775 



— Hemelytral pattern reticulate; hemelytra and face hairy 

 16 



16. Median carina well defined for entire length of pronotal 

 disc; Holarctic, northern North America 



Arctocorixa Wallengren 1894 



— Median pronotal carina poorly defined except on anterior 

 third (fig. 7:5c); United States and Canada 



Cenocorixa Hungerford 1948 



Key to California Genera of Corixidae 

 Males 



1. Pala with peg row adjacent to upper palmar bristles 

 (fig. 7:3e); face usually with dense mat of hairs (fig. 

 7:6) Graptocorixa 



— Pala with peg row separated from upper palmar bristles 

 (fig. 7:3c); face sometimes with sparse hairs but not 

 with a dense mat of hairs 2 



2. Asymmetry of abdomen sinistral (directed toward the 

 left with strigil on left side) Trichocorixa 



— Asymmetry of abdomen dextral 3 



3. Strigil absent Callicorixa 



— Strigil present 4 



4. Pala with 2 rows of pegs, the upper row sometimes 

 reduced to 2 or even 1 spine; apex of front tibia with a 

 small fleshy lobe or pad (fig. 7:9e-A); base of clavus 

 with brown bands broken or effaced (fig. 7:56) 



Corisella 



— Pala with 1 frequently curved, sinuate, or interrupted 

 row of pegs; apex of front tibia without a small fleshy 

 lobe; base of clavus with brown bands not conspic- 

 uously broken or effaced 5 



5. Lateral lobes of prothorax trapezoidal, nearly as broad 

 as long; strigil long and narrow, oriented with longitudi- 

 nal axis of body; size large, 9-11 mm.... Hesperocorixa 



— Lateral lobes of prothorax distinctly narrower than long; 

 strigil oval or transverse; size smaller, less than 8 mm. 



6 



6. Hemelytra rugose but not strongly rastrate; size rela- 

 tively large, 6.8-8 mm. (fig. 7:5c) Cenocorixa 



— Hemelytra strongly rastrate; size smaller, less than 

 6.8 mm. (fig. 7:5a) Sigara 



Key to California Genera of Corixidae 



Females 



1. Front femora with 3 or 4 tufts of long bristles or a close 

 set row of bristles subbasally on inner margin; face 



