84 MANDIBULATA. COLEOPTERA. 



terior femora compressed, dentate beneath in the males : posterior tibia? elon- 

 gate : tarsi five-jointed, the anterior in the male coarctate, dilated : claivs 

 dklactyle. 



Agabus may be known from the following genera by the form 

 and proportions of the external maxillary palpi, the compressed 

 anterior femora, the superior convexity of the body, and other less 

 conspicuous characters ; the males are further discriminated by the 

 form of their antennae, and of their anterior dilated tarsi : from the 

 foregoing genera, excepting Colymbetes, from which the palpi, &e. 

 distinguish it, the present differs by having a scutellum and swim- 

 ming posterior legs. 



f Sp. 1. serricornis. Nigro-piceus,la2vis, thoracis elytrorumque mar gine, corpora 

 subtus pedibusque rufo-piceis. (Long. corp. 5^ — 6 lin.) 



Dy. serricornis. Paykul.—Ag. serricornis. Stepk. Catal Appendix. 



Ovate, convex, obtuse ; smooth pitchy-black : head anteriorly rufo-ferruginous, 

 with two large reddish transverse spots on the crown : thorax deeply emar- 

 ginate anteriorly, very convex,, smooth, the lateral margins broadly reddish- 

 pitchy; with an irregular continuous series of impressed dots, within the 

 apex, and an interrupted one at the base : elytra very convex, the margin pale 

 ferruginous ; the superficies under a powerful lens finely but thickly punc- 

 tulate, with three irregular striae of impressed dots on each elytron : body 

 pitchy-red beneath : legs the same : the anterior femora of the male com- 

 pressed, dentate beneath, the anterior tarsi coarctate, somewhat patellate. Fe- 

 male less, with simple antennae and anterior femora. 



" Netley, Salop, rare."— Rev. F. W. Hope. 



Genus LXXXVI. — Hydaticus, Leach. 



Palpi, external maxillary with the second joint somewhat shorter than the fol- 

 lowing, the third and fourth nearly equal, the latter subulated : labrum slightly 

 emarginate : mandibles somewhat triangular, bifid : mentum trilobate. An- 

 tenna? with the second and third joints shortest, the remainder of nearly equal 

 length: head rounded: scutellum distinct: elytra ovate, convex, smooth in 

 both sexes: posterior legs natatorial : tarsi five-jointed : anterior tarsi of the 

 males patelliform and ciliated : intermediate dilated : claws didactyle : thorax 

 a little rugose in the females. 



Hydaticus was proposed as a genus by Dr. Leach, to discriminate 

 those Dyticidse that have the third and fourth joints of the external 

 maxillary palpi nearly equal in length, with the latter subulated; 

 the second and third joints of the antennae shortest; the body ovate 

 and convex ; the elytra smooth in both sexes ; the anterior tarsi of 

 the males patelliform, and the thorax somewhat rugose on the sides 

 in the females. 



