DYTISCIDAE. 95 



outer lobe absent (except in Gyrinus, where it forms an 

 iinjointed, palpus-like organ) ; anterior legs long ; the 

 liinder pairs short, first three joints of their tarsi extended 

 inward into large parchnientlike surfaces ; mesostcriuim 

 very large ; nietasternum small ; abdomen with six ventral 

 segments visi))le in both sexes, the front ones more or less 

 soldered together. Gyrinidae. 



JDYTISCmAE, 



A. Antennae ten-jointed, inserted on sides of foreliead. 



Head projecting, eyes prominent ; posterior legs not 

 compressed, only their tarsi covered with long hairs above, 

 posterior coxae dilated into a large plate, covering basal 

 half of the femora and the greater part of abdomen ; scu- 

 tellum not visible ; body thick. First tln^ee joints of male 

 front pairs of tarsi slightly dilated. Haliplides. 



J>. Antennae eleven-jointed, inserted before eyes. 



a. Head projecting. 



All the tibiae and tarsi covered with swimming hairs on 

 both sides ; posterior coxae narrow, posterior tarsi slightly 

 compressed ; scutellum visi])]e ; body thick ; third ab- 

 dominal segment projecting in middle, dividing the second 

 and first segments. First three joints of male front pairs 

 of tarsi moderately dilated. Pelohiides. 



h. Head sunk in thorax. 



Posterior coxae very large, dilated in front. 



I, Anterior tarsi apparently four-jointed. 



Front pairs of tibiae and tarsi covered on outer-side, 

 posterior pair on both sides witli swimming hairs ; front 

 pairs of tarsi apparently consisting of four joints only (of 

 wdiich three are dilated in botli sexes), the fourth joint 

 being very small and lying within the bilobed third joint ; 

 eyes not prominent ; scutellum generally hidden. 



HydroiJorides. 



II. Anterior tarsi distinctly five-jointed. 

 Anterior male tarsi more or less dilated ; eyes not 



prominent. Body flattened, Dytiscides. 



