. HYDRADEPHAGA. 63 



Plate III, Frg. 3) are found in running waters, but the ma- 

 jority frequent ponds and lakes. Many have pubescent 

 elytra ; and the surface is usually bright in the males 

 and dull in the females, a character also found in many 

 Geodephaga. 



Hyphydrus ovatus, common near London, affords a 

 good link to Pelobius, on account of its globose form, 

 and the basal joints of its tarsi being very long, as well 

 as wider than the apical joints. I have noticed that 

 fresh specimens of this insect have a smell something 

 like that of honey. 



The Dytiscides have the antennae eleven -jointed, and 

 all the feet five-jointed, the basal joints of the front legs 

 in the male being widened either simply or into round 

 plates, and the coxae of the hinder legs very large in 

 front and reaching sideways to the elytra. In the 

 genera Dytiscus, Cybister, Hydaticus, and Acilius, the 

 three basal joints of the front tarsi in the males assume 

 the form of a round sucker, fringed with hairs, with 

 little cups on the under side ; and in the first and last, 

 also, the females have the wing-cases deeply furrowed 

 longitudinally, the furrows reaching in Dytiscus half- 

 way down, and in Acilius to the apex of the elytra. 

 These two peculiarities of structure are evidently to 

 assist the sexes in pairing. The females of Dytiscus are, 

 however, sometimes found without these ciorsal furrows ; 

 and somewhat analogous instances of what is termed 

 " sexual di-morphism " occur rather frequently in the 

 genus Hydroporus, etc. 



The true Dytisci are well known, being ' ' the Water- 

 beetles " of the aquarium. They are large, olive-brown, 

 with a yellowish side-band, and very rapacious, attacking 

 all that comes in their way. They swim rapidly, diving 



