550 On Aquatic Carnivorous Coleoptera or Dytiscide. 
reticulatis, etiam ad apicem haud rugulosis, punctis seriatis magnis; prosterni 
processu lato fere plano, ad basin utrinque crassius marginato, sed haud conspicue 
longitudinaliter depresso. Long. 72 lat. 43 m.m. 
The three basal joints of the front and middle tarsi are scarcely incrassate in the 
male, but are furnished beneath with moderately long glandular hairs, the claws 
are slender and simple ; there seems to be no sexual difference in sculpture. 
The species is probably variable in colour, andis no doubt distinct from Dytiscus 
maculatus, by its very polished surface, depressed form, and less sulcate prosternal 
process : in this species also the coxal lines are more abruptly deflexed outwards 
before the apex, so that the form of the coxal processes makes a greater approxi- 
mation to what exists in Agabus. 
Japan, 836. 
I. 53.—Genus IL YBIUS. 
Posterior tarsi externally with the hind margins of their juints not straight, but 
lobate produced ; prosternal process very compressed laterally. 
This genus comprises twenty-four* species peculiar to the Northern portions of 
the Old and New Worlds; they form two groups, viz:— 
Group 1.—Hind tarsi of the male with the joints externally margined at their 
lower edge, Nos. 781 to 794. : 
Group 2.—Hind tarsi of the male not margined at the lower edge externally, 
Nos. 795 to 804. 
Group l. 
781. Dytiscus ater, De Geer, Ilybius ater, M.C_—Ovalis, elongatus, convexus, nigri- 
cans, subtus piceus, antennis pedibusque quatuor anterioribus rufis, pedibus posteriori- 
bus piceis; supra subopacus densius reticulatus, elytris guttulis duabus pallidis; coxis 
posterioribus evidenter reticulatis, margine anteriore externe parum curvato. Long. 
14, lat. 73 m. , 
The male has the three basal joints of the front and middle tarsi distinctly 
incrassate and much compressed, and clothed beneath with long hairs, bearing 
moderately large palettes ; on the front feet the anterior claw is thick, slightly 
emarginate beneath, with the extremity sharp, the posterior one being not so thick 
* And in addition to these, the names in the following list probably refer to species of this genus. 
Colymbetes fraterculus, Lec. (No. 1228); North America.—Colymbetes lateralis, Geb. (No. 1235) ; 
Siberia.—Colymbetes picipes, Kirb. (No. 1244)? near No. 789; North America.—Colymbetes ungularis, 
Lec. (No. 1256)%=No. 781; North America.—Ilybius badeni, Wehncke (No. 1470)?=No. 783; 
Germany.—llybius kiesenwetteri, Wehncke (No. 1471) ; Germany.—LIlybius ovatus, Hoch. (No. 1472) ; 
Russia.—Llybius suffusus, Crotch (No. 1473) ; North America. 
