96 ITYDTtADEniAOA — DYTISCIDAE. 



HALirLinES, 



A. Apical joint of palpi longer tluui tlie penultimate, 



conical. 



Head small, space between the large eyes narrow ; 

 thorax short, narrowed in front ; metasternum with a de- 

 j)ression ; posterior coxae covering all the ahdomen except 

 the last and the apex of the penultimate segment ; first 

 four joints of posterior tarsi gradually smaller; claws 

 small. Cnemidotus, 111. 



J*. Apical joint of palpi very small, awllike. 



a. Thorax narrowed in front ; sides nearly straight. 



Posterior coxae covering the first three abdominal seg- 

 ments, except the sides ; first four joints of posterior tarsi 

 gradually smaller ; claws small. Halvplus, Latr. 



h. Thorax nearly rectangular, sides rounded in front. 



Thorax witii a longitudinal furrow on each side, con- 

 nected at the base by a transverse furrow ; metasternum 

 with a deep, bordered depression, dividing the episterna of 

 metathorax from the coxae ; posterior coxae covering the 

 first three abdominal segments, except the sides ; first four 

 joints of posterior tarsi equal in length ; claws long and 

 "powerful. Bri/ehiu.% Th. 



(UiCtiHilotUS, 



Pale yellow, elytra grayish. Base of tliorax with a 

 sti'ong transverse impression and a row of strong punc- 

 tures ; ])unctures on elytra, ^■ery large and deep in front, 

 smaller beliind, middle of suture witli a common brown 

 spot. L. 2 1. Common. C. imjrressus, Fab. 



Ilnliphtfi, 



A, Elytra with rows of feel)le jamctures ; interstices finely 

 reticulated, irregularly punctured. 



(I, liase of thorax without any longitudinal impression 

 on each side. 



Yellow, dull ; finely punctured ; vertex of head brown. 

 Tliorax \\'ith isolated scattered larger punctures, anterior 



