On Aquatic Carnivorous Coleoptera or Dytiscide, 449 
532. Hyphydrusseptentrionalis, Gyll., Zydroporus septentrionalis, M.C.—Oblongo- 
ovalis, sine pubescentia, subtus nigricans, supra testaceus ; elytris lineis et maculis 
plus minusve interruptis et confluentibus nigris, punctis sparsis minus distinctis ; 
prothorace angulis posterioribus obtusis, utrinque striga sublaterali anterius et 
posterius abbreviata ; coxis posterioribus fortiter sed subobsolete et parce punctatis. 
Long. 35, lat. vix 2 m.m. 
The external distinctions between the sexes are extremely slight. 
This species varies in the markings of the upper surface, and also by the greater 
or less distinctness of the scattered punctures of the upper surface. The under 
surface is occasionally of an obscure ferruginous colour. In the only North 
American individual I have seen, the black colour is very conspicuous, but in form 
and the peculiar punctuation of the cox, the individual agrees exactly with 
European individuals. 
Europe. North America. In clear streams ; Sweden, Finland, Scotland, Siberia, Germany, Austria, 
Dauria, (sec. Miklin), Savoy, Grande Chartreuse, Northern Spain, (Cangas d’Onis). Lake Superior. 
230. 
533. Hyphydrus rivalis, Gyll., Hydroporus rivalis, M.C.—Latus, subrotundatus, 
sine pubescentia, subopacus, fere impunctatus ; subtus nigricans, supra testaceus, 
prothoracis disco plus minusve obscuriore, elytris lineis elongatis seepe confluen- 
tibus nigricantibus, prothorace angulis posterioribus perobtusis, utrinque striga 
sublaterali anterius abbreviata. Long. 3, lat. 2 m.m. 
The front and middle tarsi are in the male rather broader than in the female. 
This species varies extremely in colour and marking, and has sometimes a few 
fine punctures on the thorax. The under surface is sometimes obscurely ferruginous 
in colour. A very remarkable variety from the Guadarrama, entirely pale beneath 
and with the markings of the elytra obliterated, was described by meas a distinct 
species under the name of Hydroporus alienus. A variety from Lapland, (H. 
sanmarki, Sahl.) is rather more shining than those of continental Europe, and the 
lines of the elytra are very distinct. North American individuals, (Hydroporus 
obesus, Leconte), are a form in which the characteristics of this Lapland variety 
are even more exaggerated. There is thus an extreme difference between the 
Guadarrama individuals and the North American ones, but no line of demarcation 
can be traced between them when series from other localities are examined. 
Europe and North America. Lapland, Sweden and Finland, (ascending to 68° 50’ according to 
Sahlberg), Arctic Siberia, (Jenisei between 69° 30/ and 72° Sahlberg.) Scotland, England, Germany, 
Illyria; France, (Rouen, Metz, Pyrenees) ; Guadarrama. California. 229. 
