Sauropterygia. 



45 



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

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

 repi'esents 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 ot Carapace of PsepJwdei-ma alijinum, Meyer ; Trias, Bavaria 



(I nat. size). 



The oldest Chelonians known are the Ghelytherium obscurum, 

 Meyer, and Progcmochelys Queustedti, Baur, from the Triassic 

 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 Pelobatochelys, special families have been constituted. 



Wall-case, 

 No. 11. 



Order IX.— SAUROPTERYGIA. 



In this extinct order the body has no exoskeleton ; the 

 neck is more or less elongated, and the tail short. In the skull 

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

 The premaxilloG are very large, and there is a well-developed 

 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 amphicoelous (concave at both 

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

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

 culating partly on the arch and pai'tly on the centrum : these 

 have been named pectoi'al vertebrte. The ribs attached to the 

 dorsal vertebrse have the articulation entirely on the arch, 

 which generally forms an elongated transverse pi-ocess. The 



Gallery IV. 

 Wall-cases, 

 9, 10, 13.,.^ 

 Table-cases, 

 6, 7, 8. 



