4.O FOSSIL TURTLES OF NORTH AMERICA. 



Slope are found two species of the Cheloniidae and fragments of three species of 

 Trionychidae. We can not doubt that in the streams of the Mississippi Valley and 

 eastward there was an abundant population of water-loving turtles, but farther 

 westward this order of reptiles was represented principally by the land tortoises. 



During the Pliocene the land tortoises continued to predominate, especially in the 

 interior region. Three species are known from the Blanco beds of Texas. In deposits 

 of apparently the same age in Oregon there has been found a species of Clemmys. 



In the Peace Creek beds of Florida, belonging apparently to the Upper Pliocene, 

 there are found, with one large Testudo, numerous Emydidae and a species of 

 Chelydridae. These are closely related to species yet living in that region. Among 

 the numerous turtle bones put in the writer's hands from Hillsborough County, 

 Florida, are many fragments that evidently belonged to yet undescribed species of 

 Emydidae and Tnonychidae. 



In the scattered deposits of the Pleistocene, in which we might expect to find 

 remains of turtles, we discover a few species; and these present a still closerapproach 

 to those now inhabiting the same territory. In what probably corresponds to the 

 Equus, or Sheridan, beds of the region west of the Mississippi River have been 

 discovered a species of Chrysemys, 3 species of Trachemys, a species of Terrapene, 

 and 3 species of Testudo. It is worthy of note that no Testudo attains the size 

 that was reacht by species of the genus during the Miocene and the whole of the 

 Pliocene. In the Atlantic region, in caves and superficial deposits, have been found 

 remains of the snapping-turtle, the sculptured turtle, another supposed species of 

 Clemmys, and one or more species of box-tortoises. 



Briefly let us consider the geological history of the turtles of other regions. 



The earliest known turtle remains have been found in the Middle Triassic, the 

 Muschelkalk, of Germany. Huene (Palaeont. Abhandl., x, 1906) has described 

 a few cervical vertebrae which he regarded as probably having belonged to crypto- 

 diran turtles. In the Upper Triassic of the same country, the Keuper, has been 

 found Proganochelys, a nearly complete shell of which has been described by E. Fraas 

 (Jahresh. Ver. Naturk. Wiirrt., LV, 1899, p. 401). The present writer believes that 

 this turtle belonged to the Amphichelydia, and it is probable that the cervical 

 vertebrae from the Muschelkalk belonged to some turtle of the same group. 



The next oldest known turtle, known only from impressions of the carapace on 

 slabs of rock, is Protochelys stricklandi, from the Stonesfield slate, of the Great 

 Oolite, of Oxfordshire, England. It belongs probably to the Amphichelydia. 



In contrast to the scanty chelonian population of the North American Upper 

 Jurassic, that of Europe was extremely numerous. From the Jurassic at Solothurn, 

 Switzerland, about 15 species have been described. From deposits of approxi- 

 mately the same age in Germany, France, and England, numerous other species 

 have been reported. Many of the species have come from the Kimeridge, of the 

 upper portion of the Great Oolite, a formation found in England, France, and 

 Germany, and belonging near the level of the Morrison beds of Wyoming, as 

 already stated. The principal genera described from the Upper Jurassic of Europe 

 are Pleurosternon, Platychelys, Pleswchelys, Idiochelys, Hydropelta, Parachelys, 

 Acichelys, Thalassemys, Stegochelys, and Tropodemys. The first two belong 

 without doubt to the Amphichelydia, Pleurosternon being closely related to Glyptops 

 and Platychelys to Probaena. Craspedochelys and Plesiochelys are almost certainly 

 not Pleurodira and may be referred provisionally to the Amphichelydia. The 

 other genera are to be referred to the Thalassemydidae, a family of Cryptodira. 

 Similar turtles are found a little higher up in the European Jurassic, in the Purbeck 



