The Cambridge natural history . Antilles. The nucleus of theirdistribution is the Upper Tennessee Elver with its branches, andthe Coosa Eiver. They appear to dislike the neighbourhood ofthe sea, and are never fomul numerously within 100 milesof it. They adhere to stones in rapid water, and differ from theMelaniidae of the Old World and of S. America in the absenceof a fringe to the mantle and in being oviparous. They do notoccur north of the St. Lawrence Eiver, or north of in the west, or in New England. Three-quarters ofall the known species inhabit the rough square formed by th
The Cambridge natural history . Antilles. The nucleus of theirdistribution is the Upper Tennessee Elver with its branches, andthe Coosa Eiver. They appear to dislike the neighbourhood ofthe sea, and are never fomul numerously within 100 milesof it. They adhere to stones in rapid water, and differ from theMelaniidae of the Old World and of S. America in the absenceof a fringe to the mantle and in being oviparous. They do notoccur north of the St. Lawrence Eiver, or north of in the west, or in New England. Three-quarters ofall the known species inhabit the rough square formed by theTennessee Eiver, the Mississippi, the Chattahoochee Eiver, andthe Gulf of Mexico. The Mississippi is a formidable barrier totheir extension, and a whole section {Tryixmostoma, with thefour genera lo, Pleurocera, Angitrenia, and Lithasia) does notoccur west of that river. The Viviparidae are also very largelydeveloped, the genera Melantho, Lioplax, and Tulotoma beingpeculiar. The Iulmouata are also abundant, while the richness. XI NORTH AMERICA CALIFORNIA 34 I of the Unioiiidae may be gathered from the fact that Wetherbystates^ that in 1874 no less than 832 species in all had beendescribed. The entire Mississippi Imsin is inhabited by a commonassemblage of Unionidae, and a considerable number of thespecies are distributed over the whole of this area, Texas, andparts of E. Mexico. Some species have spread out of this areainto Michigan, Canada, tlie Eed Eiver, and Hudsons Bay district,and even into streams in New York which drain into theAtlantic. An entirely different set of forms occupy the greatmajority of the rivers falling into the Atlantic, the AppalachianMountains acting as an effective barrier l)etween the two groupsof species, which appear to mingle below the southern end of therange. In many cases Unionidae seem to have no difficulty inmigrating from river to river, if the distance is not extreme;they probably are carried across overflowed districts in time (2
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1895
