532 GENERAL BIOLOGY 



attaining a diameter equal to one fourth the width 



of the abdomen (i i) Dytiscus 



Front margin of the eye more or less deeply notched, 

 by the intruding margin of the front of the head; 

 stigmata nearly uniform in diameter 16 



1 6. A linear group of minute setae present upon the pos- 



tero-external angle of the hind femur (fig. 2850) . . 17 

 No such linear group of setae present . 21 



17. Claws of the hind tarsus equal, and joints simple. . 18 

 Hind tarsus with its claws unequal, and its joints 



. produced posteriorly in overlapping lobes (16) 



Ilybius 



1 8. Palpi with the terminal joint dilated, that of the 



labial palpi sub-quadrate (Calif.) (i) Hydrotrupes 

 Palpi with the terminal joint not conspicuously di- 

 lated 19 



19. Wing of the metasternum wedge-shaped 20 



Wing of the metasternum linear, and deflexed around 



the front border of the external lamina of the hind 

 coxa (8) Ilybiosoma 



20. Coxal lines very deep and nearly straight (Calif.) (i) 



Agabinus 

 Coxal lines fine and sinuous (48) Agabus 



21. Last joint of palpi emarginate at tip (3) Coptotomus 

 Last joint of palpi rounded or truncate at tip 22 



22. Prosternum with a deep median longitudinal 



groove (i) E. U. S Matus 



Prosternum not grooved 23 



23. Claws of the hind tarsi equal, movable 24 



Claws of the hind tarsi unequal, the outer one fixed 25 



24. The coxal border very broad (i) Agabetes 



The coxal border very narrow (2) Copelatus 



25. Upper surface of the body conspicuously reticulate 



(2) Scutopterus 



