WATER BEETLES (COLEOPTERA) OF OHIO1. Head anateriorly, with a frontal projection or nasale; mandibles in lateral aspect, distinctly curved upward; maxilla palp 3-segmented; urogomphus 2- segmented. Hydroporinae . . . . . 2
Head, anteriorly, without a frontal projection; mandibles in lateral aspece, not distinctly curved upward; maxillary palp with 4 or more segments; urogomphus 1- or 2-segmented. . . . . . . 17
2. Last abdominal segment with recurved extension of lateral tracheal trunks reaching beyond apex of abdomen; urogomphus very short >1/2 length of last abdominal segment. Celina hubbelli
Lateral traceal trunks not extending beyond apex of last abdominal segment, termination on apex; urogomphus of variable length. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Abdominal segment of 6 sclerotized ventrally.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Abdominal segment 6 membranous ventrally. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Urogomphus longer than abdomen; head with frontal projection without lateral branches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Desmopachria sp.
Urogomphus shorter than abdominal segment 8; heead with frontal projection with lateral branches. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Frontal projection of head elongate, constricted near base and broadly spatulate at apex, a lateral branch with 2 spines arising from each side near base. . . . . . . . . Derovatellus sp.
Frontal projection broadly triangular, not constricted near base and with or without a lateral branch on each side, althought a notch mey be present on each side. . . . . . . . . . . . . . . . . . 6
6. Larvae greatly widened in middle, greatest width approximately 0.25 of total length; leg with femur without swimming hairs; head with forntal projection witihout lateral branch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydrovatus sp.
7. Urogomphus very short, about one-half length of laast abdominal segment; last abdominal segment not constricted at insertion of urogomphi. . . . . . . . . . . . . . . . . . . . . . Lacornis sp.
Urogomphus longer, at least as long as last abdominal segment; last abdominal segment constricted at insertion of urogomphi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
8. Urogomphus with more than 7 setae (with secondary setae). . . . . . . . . . . . . . . . . . . . . . . . 9
Urogomphus with only 7 setae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
9. Last antennal segment with an anteroventral sinula and with or without a lateral pore. . . . . 10
Last antennal segment without anteroventral spinula and lateral pore. . . Hygrotus sp. (in part)
10. Maxilla with cardo absent; last antennal segment without lateral pore. . . . . . . . . . . . . . . . . 11
Maxilla with cardo present; last antennal segment with lateral pore. . . . . . . . . . . . . . . . . . . 14
11. Legs without swimming hairs; head capsule distinctily narrowed at level of occipital line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oreodytes sp.
Legs with swimming hairs; head capsule, at most, slightly constricted at level of occipital line.13
13. Head capsule broader, less than 1.3 times as long as broad. . . . . . . . . . . . . . . . Nebrioporus
14. Legs with swimming hairs. Last antennal segment without anterventral spinula and lateral pore. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hygrotus (in part)
Legs without swimming hairs. Hydroporini (in part). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
15. Urogomphus shorter, less than 2.4 times as long as last abdominal segment. . . . Hydroporus
Urogomphus more than 3 times as long as last abdominal segment. . . . . . . . . . Liodessus sp.
16. Labial palp with segments distinctly unequal; basal segment distinctly longer than second segment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uvarus sp.
17. Abdominal segments 1-6 with lateral gils; lateral margins of segment 8 and urogomphus with fringe of long setae. Coptotominae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Coptotomus sp.
Abdominal segments 1 to 6 without lateral gills' lateral margins of segment 8 and urogomphus with or without fringe of long setae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
18. Legs (femur and tibia) and lateral margins of last two abdominal segments (segments 7 and 8) with fringes of long setae or swimming hairs. Dytiscinae. . . . . . . . . . . . . . . . . . . . . . . . . 19
Legs and lateral margins of segments 7 and 8 without fringes of swimming hairs or long setae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
19. Head with anterior margin indented and appearing trilobed; uropomphus very shrot and vestigial. Cybistrini. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cybister fimbriolatus
Head with anterior margin entire; urogomphus long and apparent. . . . . . . . . . . . . . . . . . . . 20
20. Head with posterior margin deeply indented medially; anterior margin of laium between bases of labial palpi, modified anteriorly as the ligula. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Head with posterior margin at most, slightly indented medially; anterior margin of labium between bases of labial palpi, not modified, ligula absent. . . . . . . . . . . . . . . . . . . . . . . . . . 24
21. Ligula long and simple or bifid and with less than 4 apical spines; head with some stemmata greatly enlarged. Acilini. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
22. Ligula simple apically. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Graphoderus
Ligula bifid or east slightly sinuate apically. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
23. Ligula deeply sinuate apically and with short, spinelike setae. . . . . . . . . . . . . . . . . . . . Acillus
24. Urogomphus laterally without fringe of swimming hairs; head laterally with temproal spines. Hydaticini. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydaticus
Urogomphus laterally with fringe of swimmiing hairs; head laterally without temporal spines. Dytiscini. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dytiscus
25. Fore and middle legs chelate. Matinae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Matus sp.
Fore and middle legs simple. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
26. Urogomphus very short, much shorter than last abdominal segment; abdominal segment 6 sclerotized ventrally; maxillary galea spine-shaped. Agabetinae. . . . . . . . . . . . . . Agabetes
Urogomphus longer, subequal to or much longer than last abdominal segment; abdominal segment 6 sclerotized ventrally or not; maxillary gleae fiinger-or hook-shaped. . . . . . . . . . 27
27. Mandible with large and distinct teeth along inner margin and not grooved internally; maxillary galae hook-shaped; uropomphus with one segment; legs without swimming setae. Copelatinnae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Copelatus
Mandible without large and distinct teeth along inner margin and grooved internally or not; maxillary galea fingerlike; urogomphus with one or two segments; legs with or without swimming hairs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
28. Apical antennal segment biramous and consisting of two unequal lobes; urogomphus 2- segmented and with many more than 7 hairs. Lacophilinae. . . . . . Laccophilis sp.
Apical antennal segment simple and uniramous, uroponphus 1- or 2-segmented and with only 7 hairs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
29. Urogomphus with a subbasal suture and with secondary setae; occipital line present; legs with swimming setae present on dorsal margin of either femur, tibia and tarsus or tarsus only. Colymbetinae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Urogomphus without a subbasal suture and with or without secondary setae; legs with swimming setae absent or if present on dorsal margin of tibia and tarsus . Agabinae. . . . . 32
30. Tibia and femur with swimming hairs; tarsal claw with pinulae (amall spines on lower margin in basal half) well developed; prementum with anterior margin straight or slight concave. . . . . 32
Tibia and femur without swimming hairs; tarsal claw without spinulae or poorly developed; prementum with anterior margiin deeply emarginate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
31. Last abdominal segment elongate; subequal to or longer than width of head; smaller segments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rhantus sp.
Last abdominal segment shorter, length less than width of head; larger segments. Colymbetes
32. Tibia and tarsus with natatory setae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Agabus (in part)
Tibia and tarsus without natatory setae. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
33. Abdominal segment 6 sclerotized ventrally. . . . . . . . . . . . . . . . . . . . . . . . . . Agabus (in part)
Abdominal segment 6 membranous ventally. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
34. Urogomphus with only 7 setae (without secondary setae). . . . . . . . . . . . . . . . . . . . . . . . . 35
Urogomphus with more than 7 setae (with secondary setae). . . . . . . . . . . . . . . . . . . . . . . 36
35. Last abdominal segment longer, more than 3/4 as long as head. . . . . . . . . . . Ilybius (in part)
Last abdominal segment shorter, about 1/2 as long as head. . . . . . . . . . . . . Agabus (in part)
36. Urogomphus with 7 primary hairs in 2 whorls, 3 near middle, 4 apically. . . . . . . . . . . . . . . . 37
Urogomphus with only apical whorl distinct; basal whorl with setae distinctly separated. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Agabus (in part)
37. Lateral margin of head more or less compressed or keeled, temproal spines oon a line that would intersect stemmata or just pass below them. . . . . . . . . . . . . . . . . . . . Ilybius (in part)
Lateral margin of head not keeled, temporal spines on a line that would run well below stemmata. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Agabus (in part)
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Key to Dytiscidae Nymph Genera