GEOLOGICAL DISTRIBUTION. 39 



similar that there is no wonder that the faunae did not dift'er greatly. In the Laramie, 

 as in the Judith River, there were Baenidae and Trionychidae. The Dermate- 

 mydidae are represented by at least one species, Basilemys sinuosa, not greatly 

 different from B. vartolosa of the Judith River. The Pleurodira appear to be 

 represented by one species, Naiadochelys ingravata, from New Mexico. 



On entering the Tertiary there is no striking change in the turtle fauna. In the 

 Fort Union, the Puerco, and the Torrejon, there are yet Trionychidae, Dermate- 

 mydidae, and Baenidae. Representatives of the same families pass up into the 

 Wasatch. Here, however, new elements enter, the Emydidae and the Testudinidae. 

 It is not improbable that Gyremys spectabihs of the Judith River beds is an emyd, 

 but the group is unmistakably represented in the Wasatch by Echmatemys, a genus 

 in some respects highly specialized. '1 he Testudinidae are represented by the 

 genus Hadrianus, the oldest-known genus of the family. All these Wasatch turtles 

 inhabited either the land or the fresh waters of streams. 



In the Atlantic region we have nearly contemporaneous deposits; and in them 

 we find fragmentary remains of a few probably marine turtles and of Trionychidae. 



The Wind River beds have so far furnisht only a single species of Bapternys, and 

 the humerus, 187 mm. long, of a trionychid. 



The Bridger beds of Wyoming are exceedingly rich in turtle remains, as they 

 are also in the bones of crocodiles and mammals. The Baenidae were numerous in 

 species and individuals. Only 2 genera of dermatemyds have been found. Emy- 

 did;e abounded, and Trionychidae ran riot. In addition to these there were a few 

 species of Plastomemdae. All together, there are 50 or more species of turtles 

 described from the Bridger Eocene. The abundance of Baenidae and especially 

 of the Trionychidae shows that there were numerous streams and lagoons; and this 

 conclusion is confirmed by the presence of many species of crocodiles. The occur- 

 rence of the great turtle Hadrianus seems to indicate the proximity of dry land. 



Nearly all the species of Bridger turtles occur in the lower portion, that known 

 as level B. No turtles have yet been described from the limestone bands, but 

 fragmentary remains occur there. These bands appear to have been laid down in 

 shallow lakes. 



So far as known the turtles of the Uinta beds belong to genera found in the 

 Bridger beds. No Plastomenidae have been found, and the Baenidae appear for the 

 last time in our calendar. 



During the Oligocene epoch the scene, for the student of turtles, shifts from the 

 sea shore and the mountain regions to the Great Plains. In the lowest division, the 

 Chadron or Titanothenum beds, are found I trionychid, I dermatemyd, and 

 i emyd, silent witnesses of the presence of streams. On the other hand, there were 

 numerous species of Testudinidae, or dry-land tortoises, some of which attained a 

 large size. Of Stylemys nebrascensis great numbers of shells have been found in 

 South Dakota and Colorado, in the Brule clays, or Oreodon beds. Species of 

 Testudo were more abundant in the same deposits in Colorado. There can be no 

 doubt that at this time the climate of the Plains region had become arid and the 

 streams few. A similar climate appears to have prevailed in the John Day region 

 of Oregon, where 2 or 3 species of Stylemys abounded, but, so far as known, no 

 other turtles. 



The Miocene deposits of the interior of the continent are characterized by the 

 presence of species of Testudo, many of them of large size, resembling the gigantic- 

 tortoises of the Galapagos Islands. Sixteen species are described. In the Middle 

 Miocene of Oregon there has been found a species of Clemmys (C. saxea); in the 

 Upper Miocene of Kansas, Trachemys htlli. In the Yorktown beds of the Atlantic 



