File:Image from page 257 of "Water reptiles of the past and present" (1914) (14769947901).jpg

Identifier: waterreptilesofp1914will Title: Water reptiles of the past and present Year: 1914 (1910s) Authors: Williston, Samuel Wendell, 1851-1918 Subjects: Aquatic reptiles Publisher: Chicago, Ill., The University of Chicago Press Contributing Library: Boston Public Library Digitizing Sponsor: Boston Public Library

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Text Appearing Before Image: heir own, the Trionychoidea, especiallydistinguished from the Cryptodira, whichin general they resemble in most respects,aside from the absence of the usual hornydermal plates, in the lack of a marginalrow of bony plates around the carapace—not a very important distinction. Lessthan thirty living species are known, allof them exclusively or chiefly of fresh-water habit. Six species are known fromNorth America; the remainder inhabitAfrica, south of the Sahara Desert, southern India, and most ofthe East Indian islands; none is known from Australia. Nospecies lives in South America and none is known to have livedthere in past times. During Eocene, Oligocene, and Miocene timesthese fresh-water turtles lived in the region of Europe in greatnumbers, but for some inexplicable reason they became extinctthere and never returned. Nearly seventy species of the Triony-choidea, belonging in two families, are described by Dr. Hay fromthe Tertiary rocks of North America, more than twice the number

Text Appearing After Image: Fig. 130.—Aspideretes, atrionychoid turtle fromthe Basal Eocene of NewMexico; skull from above.(From Hay.) CHELONIA 247 now living throughout the world. Some of these were of relativelylarge size, measuring fully two feet in the length of the shell.And in some places they must have been veryabundant. The writer has seen, in the BadLands of the Continental Divide, theirweathered-out remains so numerous that theymight be raked into windrows miles in lengthalong the sloping bluffs, all in small frag-ments, for their bones, like those of mostturtles, are only loosely united by suturesand readily drop apart before fossilization.Their shells may be readily distinguishedfrom those of all other turtles by the granu-lated, pitted, or sculptured exterior surface,that was covered by the skin in life; otherturtles have the surface smooth below thehorny shields, the margins of which aremarked on the bones by grooves or sulci;the few marine turtles of the past that wereprobably covered with a sof

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