. Süßwasser-Biologie. Süßwasser-Biologie. 846 Süßwasser-BIOLOGIE 34 (29) Körper subcylindrical in seinem vorderen Teil, Bauch gedrückt. Ros-trum deprimiert. Pleura der zweiten abdominal Segment nicht die Überlappung vor. Die ersten drei Paare von peraeopods Chelat, das erste Paar viel größer als die anderen. Familie Potamobiidae 35 Eine exklusive Süßwasser-Familie von Alter und die wichtigste Gruppe von höheren Crusta - odile im Süßwasser von Nordamerika. Ihre allgemeine Verbreitung umfasst Europa, Nord-östlichen Asien, Nord- und Mittelamerika. In den Vereinigten Staaten zwei Gattungen zu finden sind:

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. Fresh-water biology. Freshwater biology. 846 FRESH-WATER BIOLOGY 34 (29) Body subcylindrical in its anterior part, abdomen depressed. Ros- trum depressed. Pleura of second abdominal segment not overlapping those in front. First three pairs of peraeopods chelate, the first pair much larger than the others. Family Potamobiidae 35 An exclusive fresh-water family of old age, and the most important group of higher crusta- ceans in the fresh waters of North America. Its general distribution includes Europe, north- eastern Asia, North and Central America. In the United States two genera are found: one, containing a few species, is believed to be identical with the European genus (Poiamobius); the other (Cambarus) is restricted to America, and has very many species. The differences of these genera are found chiefly in the sexual apparatus. In the southern hemisphere, in Australia, New Zealand, South America, and Madagascar this family is represented by an allied one, Parastacidae while in the tropical belt similar forms are missing. This pecuUar distribution has given origin to much speculation, and chiefly the close affinity of the southern forms has been introduced as evidence for the former connection of the southern continents. Through Huxley's book (1880) this family has become a standard group for biological study. 35 (36) Male copulatory organs rather simple. Peraeopods of male without hooks on the ischiopodite. Female without receptaculum seminis. A pleurobranchia present on the last thoracic somite. ... ... Potamohius Leach. This is the genus which includes the Euro- pean crayfishes, frequently, but incorrectly, called Astacus. It possesses five species in North America, the range of which is on the western Pacific slope, from California to British Columbia. One species (P. gambeli Girard), has crossed the continental divide in the region of Yellowstone Park, and is found on both sides in the drainages of the upper Columbia River and of the upper Missouri. The Eu

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• bookcentury1900
• bookdecade1910
• booksubjectfreshwa
• bookyear1918