938 



FRESH-WATER BIOLOGY 



7 (4) Last abdominal segment elongate pyramidal, and furnished with a mid- 



ventral line of hairs Gyretes. 



8 (3) Hind legs longer than the fore; eyes 



two 9 



9 (14) Base of the hind legs covered by broad 



overlapping coxal plates. 



Family Haliplidae 10 



10 (13) Coxal plates concealing only the three 



basal segments of the abdomen; 

 last segment of palpi shorter 

 than the preceding segment. 1 1 



11 (12) Pronotimi widest before the middle. 



Brychius. 



12 (11) Pronotmn widest at the rear end. 



Haliplus. 



13 (10) Coxal plates concealing all but the last 



of the ventral abdominal seg- 

 ments; last segment of palpi 

 longer than the preceding seg- 

 ment. Peltodytes. 

 14(9) Base of the hind legs exposed . ... 15 



15 (48) Antennae shorter than the palpi; legs 



usually with swimming fringes. 

 Family HvDROPHiLiDAE . . 16 



16 (23) Scutellum wanting or indistinct or very 



small and scalelike. Posterior 

 femora subcyhndrical and not 

 noticeably widened in the mid- ^ ^. 



ji .-L J T_ 1 - 1 iTG. 1392. Diagram 01 the ventral 



die ; pro thorax narrowed behind, aspect of a diving beetle, Capiotomus 



narrower than the elytra. The i^^^rogatus: a, antenna; i, mouth; 



n 1 J. ^' '■• coxal cavities for the fore and 



species are small, elongate, middle legs; d, labial palpi; e. eye; 



roughly sculptured, greyish or J. maxillary palpi; 5, lateral margin 



111 1 J n V. • 1 ot the prothorax; h, epipleuron of 



nearly black, and usually tinged the wing cover (elytron); ;, pros- 



With bronze and metallic col- ternal process; /, metastemal fork; 



17 (20) 



18 (19) 



19 (18) 



ors. ... . . . 17 



ScuteUum indistinct, or apparently want- 

 ing; if at all evident it is 

 distinctly triangular and acute. 

 Species from 1-2 mm. long. 18 

 Pronotum without striae; maxiUary palpi 



k, hind coxa with /, the inner lam- 

 ina; p, the coxal process and g, the 

 coxal notch; r, trochanter of the 

 hind leg; s, femur; t, tibia; u, hind 

 tarsus of five joints; j, 2, 3, 4, ?, (5, 

 ventral abdominal segments, 5^^, 5P, 

 if, sterna of pro-, meso-, and meta- 

 thorax, respectively; wj, wing of the 

 metasternum; m, episternum, and 

 «, epimeron of the successive thor- 

 as long as the head and thorax ?™ segments. The coxal line is the 

 . .1° .1 1^. , , line extending between / and k in 



together, the ultimate segment the figure, and the raio/Jor&r is the 



longer than the penultimate; pa" of the coxal proce^, ? , that is 



1 7 •, i_ .1 ^ ' marked off laterally by the postenor 



elytra with more than ten rows end of the coxal Une. 

 of punctures. . . . Hydraena. 



Pronotum bearing from one to five longitudinal striae or abbreviated 

 grooves; the maxiUary palpi much shorter than the head 

 and thorax together, the ultimate segment shorter than the 

 penultimate; elytra with only ten rows of punctures. 



Octhebitts, 



