1 84 



THE EXTINCT BATRACHIA, REPTILIA 



genus, but one is probably figured by Camper (Tab. 2 IS, fig. 21 of Cuvier Ossem. Fossiles), 

 which Cuvier says is perhaps an ungueal phalange. The dorsals have no hypapophysis, 

 and the diapophyses decrease in vertical extent towards the posterior part of the series. 

 The greatest variation is presented by the different species in the long series preceding 

 the eaudals, which do not present zygapophyses. The posterior of this series arc much 

 shorter than the anterior, the former having the form of the dorsals, the latter of the eau- 

 dals. In the M. dekayi, ML gracilis and M. giganteus, none of these are depressed ; the 

 shorter are subpentagonal in section; in M. depressus and M. missuriensis the longer are 

 depressed, while the depression of the shorter diminishes regularly to the distal cau- 

 dal series. In M. brumbyi the Ion-' vertebrae are flattened to a still greater degree. 

 (See Gibbes' Mongr.) 



The eaudals an; divided into three series by Cuvier, viz: those with separate chevron 

 bones, those where the latter are united to the centrum, and those without them. Pass- 

 ing posteriorly these; vertebra become gradually shorter and more vertically ovate in form. 

 The more posterior are less narrowed in the M. maximus, M. oarthrus and M. missuriensis 

 (vide Leidy's work), while in M. dekayi and the Liodons they are rather more; narrowed 



vertically. 



The characters of the diapophyses are marked in different parts of the column. In 

 all the species of the family they descend from an elevated position on the ccrvicals and 

 anterior dorsals to an inferior one on the lumbars. They nevertheless never spring from 

 the neural arch, as in the Archosanria, but always from the base o( it. On the median 

 dorsals it originates from the middle of the side of the centrum, and on tin; lumbo-sacrals 

 from the plane of the inferior surface. It diminishes in size, and as soon as the articula- 

 tions of the chevron bones appear, begins to ascend again. On the anterior eaudals it 

 rises to near the middle of the centrum and gradually disappears, at different points in the 

 different species. 



The chevron bones are free throughout the anterior part of the caudal series in the M. 

 "■io'autens. and confluent with the centrum in the posterior portions. This is probably the 

 rase with many species of the "'onus. During immaturity they may bead distinct in Mo- 

 sasanrus, and in the genus Liodon (vol Macrosaurus) this condition is permanent through- 

 out life, and so characteristic This is indicated by the very large individual typical of 

 L proriger, and is visible in two other species of the genus; 



Genera. The four genera below enumerated appear to differ in tangible characters, 

 These are found in the relations of the pterygoid bones and teeth, and characters of verte- 

 bras. A number of genera have been proposed on minor modifications in the forms of the 

 teeth. These are Liodon,, Owen, Holcodtts, Gibbes, and Polygonodon and Pliogonodon 

 of Leidy. The very close similarity in dental characters among the members of this 



