188 ADEPHAGA. \_Cuhjmhdina. 



limited number of genera the best plan would seem tO be to regard the 

 Colymbetina as one tribe including the genera Agahus. Platamhus, 

 IJi/Mus, Cox>elatns. Rhantus, and Colymbetes, the genus Cojiclatus forming 

 a transition between the first three and the last two ; they may then 

 be divided as follows : — 



I. Posterior external angle of hind femora furnished with a 



little group of cilia. 



i. Claws of posterior tarsi unequal Iltbius, Er. 



ii. Claws of posterior tarsi equal. 



1. Wings of metasternum variable in size but always 

 distinctly wedge-sliaped, never linear ; epipleurae of 



elytra narrower Agabtjs, Leach. 



2. Wings of metasternum sleuder and linear ; epi- 



pleuraj of elytra flat and broad behind middle . . . Piatambus, Thorns. 



II. Posterior external angle of biud femora without group of 



cilia. 



i. Claws of posterior tarsi equal Copelattjs, Er. 



ii. Claws of posterior tarsi unequal. 



1. Sides of thorax margined ; elytra not transversely 



striolate RhantuS, Lac. 



2. Sides of thorax not margined ; elytra transversely 



striolate Colymbetes, Clairv. 



AG-ABUS, Leach. 



In this genus the sides of the prothorax have a raised margin, and the 

 terminal joint of the palpi is not thickened ; the genus comprises about 

 a hundred species from Europe, Northern Asia, and North America, 

 and a considerable number of species standing under other generic 

 names are probably referable to it ; it is very difficult to determine the 

 species, as they are so much alike in general appearance, although in 

 obscure points of structural difference they vary exceedingly from species 

 to species: the following table may be found of some service, but in each 

 case the more minute differences must be carefully compared : the 

 species are of moderate size, being on an average about 8 or 9 mm. 

 long, and are either black, bronze, or lighter or darker testaceous, uui- 

 colorous, or with a variety of markings ; the sculpture of the elytra nearly 

 always consists of a fine reticulation, the size and shape of the meshes 

 often affording a good character for the distinction of the species ; on 

 each elytron there are usually two or three irregular rows of large 

 punctures, which however are sometimes very indistinct in the dull 

 females. 



The larva of Plafamhus {Agahus) maculatus is figured by Schiodte (ii., PI. vi., 

 Fig. 1) : it is elongate-ovate, somewhat depressed, strongly acuminate behind, pale, 

 with the head and the dorsal scuta fuscous-bhick spotted and marked with whitish- 

 yellow ; head narrow almost orbicular, prothorax narrower than mesothorax with 

 sides very strongly rounded, narrowed in front ; seventh and eighth abdominal seg- 

 ments very narrow, cylindrical, cerci very long proceeding from the apex of the 

 eighth segment, furnished in middle and at apex with loug setae; legs rather long 

 with very long equal claws. 



