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7. 31 Chas. Jovey Simpson On the Mississippi Valley Unionidae found in the St. Lawrence and Atlantic Drainage Areas. [[strikethrough]] By The [[/strikethrough]] Am [[strikethrough]] erican [[/strikethrough]] Naturalist, xxx, No. 353, May 20, 1896, pp. 379-384. This paper shows that the extralimital Mississippi Valley Unionidae found in the St. Lawrence basin are usually dwarfed and dull colored, and claim is made that many of the so-called species of the latter region are merely depauperate varieties of well known Mississippi Valley forms which have become changed since they have occupied the waters they now inhabit. The theory is advanced that these species migrated northward at the close of the glacial epoch, by way of old streams that flowed from lakes in the north into the Mississippi Valley at the time, as the ice cap to the North and Northeast prevented drainage to the North and east. Description of Four new Species of Unios from the Staked Plains of Texas. [[strikethrough]] By [[/strikethrough]] Charles Forrey Simpson. Proc. U.S. Nat. Mus. XVIII, No. 1072. May [[strikethrough]] 20 [[/strikethrough]] 19th, 1896, pp. 387-385, figs 1-5. [[strikethrough]] m text [//strikethrough]] This is a description of Unios believed to be Triassic. These four forms exhibit a remarkable diversity in from, sculpture, hinge and other characters and indicate that the genus Unio had long been established at the time these species were living. Specimens from the type lot and caste from types are in the Museum Collection.