200 



REPTILIA 



CLASS III 



Nuchal without costiform process. Plastron connected with carapace by axillary 

 and inguinal buttresses. Humerus with imperfectly developed head and nearly straight 

 shaft. ' Phalanges with articular condyles, all the terminal ones clawed. Upper Jura 

 and Cretaceous. 



This family includes a number of Mesozoic genera which combine the 

 characters of both marine and marsh turtles, and are probably directly 



ancestral to the Chelonidae. They 

 appear to have been mainly of marine 

 habits. The very incomplete ossification 

 of the carapace and persistent fontanelle 

 of the plastron present the same conditions 

 as in sea-turtles, while the form of the 

 plastral elements and the outwardly bent 

 extremities of the hyo- and hypo-plastrals 

 are suggestive of marsh forms. The five 

 functional toes with articulating phalanges 

 were all clawed and probably webbed in 

 life, having been adapted for both pro- 

 gression on land and for swimming. 



Thalassemys, Rut. (Enaliochelys, Seeley). 

 Carapace moderately thick, flattened, with 

 well-ossified pleurals, the posterior neurals 

 not forming a tectiform ridge. Vertebral 

 shields narrow. Very large persistent 

 vacuities in the plastron. Upper Jura ; 

 Switzerland and England. 



Eury sternum, Wagler (Achelonia, 

 Acichelys, Aplax, Palaeomedusjx, v. Meyer ; 

 Euryaspis, Wagner), (Fig. 303). Carapace 

 flattened, distinctly emarginate anteriorly, 

 with the pleurals well ossified and pos- 

 terior neurals not forming a tectiform 

 ridge. Vertebral shields very wide, mar- 

 ginals long and narrow. Plastron with large persistent vacuities. Upper 

 Jura (Lithographic Stone) ; Bavaria and Cerin, Ain. 



Tropidemys, Rutimeyer ; Pelobafochelys, Seeley. Upper Jura and Wealden ; 

 Europe. 



Cliitracephalus, Dollo. Cranium much elongated and depressed, with an 

 extremely short facial region, and temporal fossae not roofed. Cervical 

 vertebrae without transverse processes. Pleurals narrowed at their outer 

 ends, with vacuities within the well-developed border of the peripherals. 

 Plastral elements similar to those of Chelone. Digits clawed, not greatly 

 elongated. Wealden; Belgium. C. dumoni, Dollo. 



Fig. 303. 



Ewystemum wagleri, v. Meyer. Upper Jura 

 Zandt, near Eichstadt, Bavaria. 1/3. 



Family 2. Chelydridae. 



Agassiz. 



Temporal region of skull incompletely roofed over ; no parieto- squamosal arch. 

 Frontals excluded from orbit ; maxilla separated from the quad ratoju gal ; squamosal 

 in connection with postorbito-frontal. Epidermal shields absent in some cases : number 

 if neurals complete ; posterior pleurals meeting in the median line. Shell usually not 



