32 Key to Families of North American Insects. 



12. Maxillary palpi slender, almost always as long as or longer than the antennae; 



antennae six- to nine-jointed, the outer joints forming a pubescent, distinct 

 club; usually aquatic, convex beetles. Larvae usually with cerci. (Pal- 

 picoRxiA.) Water scavenger beetles. (Hydrophilus, Laccobius, Hydrobius, 



Cercyon) (PI. C, figs. 110, 111) HYDROPHILID^ 



Maxillary palpi much shorter than the antennae; larvae never with cerci. (Di- 

 VERsicoRNiA, PoLYMORPHA, or Clavicornia and Serricornia) 13 



13. Elytra short, exposing much of the abdomen; dorsal segments of abdomen 



entirely horny in texture; wings usually present and folded beneath the 



elytra, crossveins absent 14 



Elytra covering most of the abdomen, rarely much shortened, in which case 

 the wings are wanting, or not folded beneath the elytra; dorsal segments 

 partly membranous 15 



14. Abdomen flexible, seven or eight ventral segments, body usually slender; 



scavengers. Rove beetles. (Stenus, StaphylTnus, Tachyporus, Philonthus) 



(PI. 5, fig. 95) .STAPHYLINID.E 



Abdomen not flexible, five or six ventral segments; small or minute, robust 

 beetles. (Bryaxis, Batrisodes) (PI. 7, figs. 138, 148) . . . PSELAPHEDjE 



15. Tarsi five-jointed on at least one pair of legs, and almost always on all pairs . . 16 

 All tarsi with less than five joints 65 



16. Last tarsal joint long and with very large claws (PI. 7, fig. 143); first three 



ventral segments grown together; small aquatic or subaquatic beetles. 



(Psephenus, Dryops, Ehnis) {DRYOPIDM) PARNIDiE 



Tarsal claws normal; all ventral segments free except in the Colydiidae, Heter- 

 oceridae, Buprestidae and some Byrrhidse which are not aquatic 17 



17. Abdomen with five ventral segments 18 



Abdomen with at least six ventral segments 50 



18. Front coxae globular or transverse, usually projecting but little from the coxal 



cavity; trochanters never interstitial 19 



Front coxae more or less conical and prominent 37 



19. Front coxae transverse, more or less cylindrical , 20 



Front coxae globular 27 



20. Hind coxae grooved to receive the femora 21 



Hind coxae flat and not grooved 26 



21. Strongly convex beetles with more or less retractile legs, tibiae dilated and 



usually grooved near the outer end to receive the tarsi, tibial spurs dis- 

 tinct 22 



Slightly convex oval species with non-retractile slender legs; tibial spurs more 

 or less reduced 24 



22. Antennae inserted at sides of head 23 



Antennae inserted on front, head retracted; third tarsal joint lobed; thorax 



margined; oval tropical species (Chelonarium) CHELONARIID.^ 



23. Head prominent, mentum large, elongate and subelliptical; tarsi not lolxnl. 



(Nosodendron.) NOSODENDRIDiE 



Head retracted, mentum small and quadrate; (Amphicyrta, Byrrhus). 



BYRRHIDiE 



