On Aquatic Carnivorous Coleoptera or Dytiscidce^ 449 



532. Hypliydrus septentrionalis, Gyll. , Ilydrovorus 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. 3h, lat. vix 2 m.m. 



The external distinctions between the sexes are extremely slight. 



This species varies in tiie 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 coxiB, the individual agrees exactly with 

 European individuals. 



Europe. North America. In clear streams ; Sweden, Finland, Scotland, Siberia, Germany, Austria, 

 Dauria, (sec. Maklin), Savoy, Grande Chartreuse, Northern Spain, (Cangas d'Onis). Lake Superior. 

 230. 



533. Hyphj'drus rivalis, Gyll., Hydroporusrivalis,M.C. — Latus, subrotundatus, 

 sine pubescentia, subopacus, fere impunctatus ; subtus nigricans, supra testaceus, 

 prothoracis disco plus minusve obscuriore, elytris lineis elongatis ssepe 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 me as 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 G9° 30' and 72° Sahlberg.) Scotland, England, Germany, 

 Illyria : France, (Eouen, Metz, Pp-enees) ; Guadarrama. California. 229. 



