Sauropterygia. 



45 



head and some other parts of the skeleton may be seen Wall-case, 

 and compared, is from the London Clay of Sheppey, and No. 12. 

 represents a still larger form related to the living Leathery 

 Turtle. These were true marine turtles, like the " Logger- 

 head " Turtle of the present day (Fig. 59). 



FIG. 60. Fragment ol Carapace of Psephodenna alpinum, Meyer ; Trias, Bavaria 



(J nat. size). 



| 



The oldest Chelonians known are the Chelytherium obscurum, Wall-case, 

 Meyer, and Proganochelys Quenstedti, Baur, from the Triassic No * 11 - 

 sandstones, Stuttgart. 



Of the fifty-two genera and one hundred and thirty- one 

 species or varieties of fossil Chelonians named in the collection, 

 only eighteen genera and ten species can be with certainty 

 correlated with living forms ; whilst for the reception of a 

 few of the more remarkable extinct forms, such as Miolania 

 and PelobatocJielys, special families have been constituted. 



Order IX. SAUROPTERYGIA. 



I 



In this extinct order the body has no exoskeleton ; the Q-allery IV. 

 neck is more or less elongated, and the tail short. In the skull W to"is Se - S> 

 the nares, or nostrils, are lateral and placed near the orbits. Table-coses 

 The premaxillae are very large, and there is a well-developed e, 7, 8. 

 parietal foramen in the adult. The symphysis of the mandible 

 is united by a suture (Fig. 63) . The teeth are implanted in 

 distinct sockets and confined to the margins of the jaws ; they 

 have curved sharp crowns with fluted enamel. Each rib articu- 

 lates to a single vertebra ; the facets for the cervical ribs may be 

 either single or double, and are situated entirely on the 

 centrum. The vertebrae are amphiccelous (concave at both 

 ends). The neck may have as many as from 21 to 44 vertebrae. 

 A few of the vertebras behind the cervicals have the ribs arti- 

 culating partly on the arch and partly on the centrum : these 

 have been named pectoral vertebras. The ribs attached to the 

 dorsal vertebrae have the articulation entirely on the arch, 

 which generally forms an elongated transverse process. The 



