WATER BEETLES IN RELATION TO PONDFISH CULTURE. 
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11. Prothorax two or three times as long as wide; cerci short and naked; labium with a large ligula; 
stipes of maxilla as long as the palp 12 
11. Prothorax a little longer than wide; cerci half the length of the abdomen and densely plumose; 
labium without a ligula Laccophilus. 
11. Prothorax considerably wider than long; cerci long and plumose; labium without a ligula; maxillary 
palp much longer than stipes 13 
12. Ligula tipped with two long, jointed spines Thekmonectes. 
12. Ligula without terminal spines Acilius. 
13. Larger, 15 to 20 mm.; cerci densely plumose 14 
13. Smaller, 8 to 12 mm.; cerci with scattered hairs only 15 
14. Maxillary stipes slender, with concave sides, armed on the inner margin with a long seta and a 
single spine Colymbetes. 
14. Maxillary stipes stout, with convex sides, armed on the inner margin with two or three spines 
and a row of setae Rhantus. 
15. Maxillary stipes armed on the inner margin with two long curved claws and many small spines and 
setae Ilybius. 
15. Maxillary stipes armed on the inner margin with small spines and setae only; no curved claws. 
Agabus. 
16. Body segments with filiform tracheal appendages as long as the body itself; tip of abdomen 
bluntly rounded Peltodytes. 
16. Body segments with short triangular appendages; tip of abdomen acuminate, ending in two 
filiform, jointed setae Haliplus. 
17. Epicranial suture wholly lacking; each mandible with a terminal seta, a simple lobe or lacinia 
mobilis, and an inner tooth Hydrochous. 
17. Epicranial suture present; mandibles without a terminal seta or a lacinia mobilis, but with one or 
more inner teeth 18 
18. Abdomen with seven pairs of long lateral filaments, which serve as tracheal gills; mandibles 
with two or three teeth 19 
18. Tracheal gills reduced to mere tubercles or wanting; mandibles with only one or two teeth 20 
19. Second joint of antenna with finger appendage outside of the terminal joints; no stigmatic atrium at 
tip of abdomen Berosus. 
19. No finger appendage on antenna; ninth and tenth abdominal segments forming a stigmatic 
atrium Hydrophilus . 
20. Second joint of antenna with finger appendage outside of the terminal joint; mandibles not 
grooved internally ; femora without a fringe of swimming hairs 21 
20. No finger appendage on the antenna; mandibles definitely grooved internally; femora with a 
fringe of long swimming hairs 22 
21. Labium without a ligula; tarsus as long as the tibia Laccobius. 
21. Labium with a ligula, which is longer than the basal joints of the palpi; tarsus much shorter than the 
tibia Philydrtjs . 
22 . Mandibles each with a single inner tooth ; ligula not as long as the basal j oints of the palps. 
Hydrous. 
22. Mandibles each with two or more inner teeth; ligula distinctly longer than the basal joints of 
the palps Tropisternus. 
KEY FOR IDENTIFICATION OF PUP/E. 
1. Tibiae of first two pairs of legs folded tightly against the femora and the two inclined forward at an 
angle of 45° with the body axis; knees projecting strongly and armed with spines; antennae folded 
across the eyes; no posterior cerci HALIPLIDJD 2 
1. Femora at right angles to the body axis, tibiae not folded against them; knees neither projecting nor 
armed with spines; antennae not crossing the eyes; a pair of stout posterior cerci, jointed or bifid; 
etyli long and jointed, with an enlarged basal portion HYDROPHILIDiE 3 
1. Femora at right angles to body axis, tibiae not folded against them; first pair of knees projecting but 
not armed with spines; each compound eye divided into a dorsal and ventral half, separated some- 
what; no posterior cerci; styliin the form of short bristles, not jointed GYRINIDJS 8 
