CRANIAL AND VERTEBRAL CHARACTERS OF PLESIOSUCHUS. 153 
6. On the CRantaL and VERTEBRAL CHAracterRs of the CROCODILIAN 
Genus Puustosucuus, Owen. By Sir Ricnarp Owen, K.C.B., 
F.R.S., F.G.8., &. (Read November 21, 1883.) 
In the ‘ Preliminary Remarks’ to the paleontology of the Croco- 
dilian Reptiles, Cuvier urges the need of a precise determination of 
the generic characters, with regard to which he writes, “‘observations, 
however novel, lose all their merit, unless they rest on this basis” *. 
He proceeds to exemplify the apophthegm by descriptions which 
have never been surpassed of new and interesting species of extinct 
Reptiles, especially Crocodilian, which he shows to have been erro- 
neously referred to other previously defined genera. 
Cuvier refrained from attaching generic names, distinct from 
those of his “ subgenera” of existing Crocodiles, to the extinct forms 
of which his keen and careful observations had detected characters 
since generally admitted to merit such distinction, and of which a 
contemporary availed himself. 
The characters which Cuvier defines as forming for the Crocodiles 
a‘‘ very natural genus” { are now recognized as defining an ordinal 
group of the class Reptiliat. But of this group he admits and 
names “Subgenera,’, and to their distinctive characters he devotes 
special ‘* Sections,” as, for example, ‘‘ 1°, Espéces de Caymans ” 
(p. 30); “‘IL°, Especes de Crocodiles ” (p. 42); “ III°, Espéces de 
Gavials” (p. 59). Our Catalogues accordingly admit these groups of 
Crocopizia, under the generic names Alligator, Crocodilus, Gavialis. 
In the Srcrion III, “Sur les Ossemuns Fosstzes de Crocodiles,” 
the vertebral, dental, and narial characters of the extinct species are 
defined, and those of the ‘ Secondary” or “‘ Mesozoic” formations 
are of higher value than he assigns to his recent ‘* Subgenera ;” but 
he forbears to invent special terms for the extinct groups so differ- 
entiated. He even expresses a doubt whether the fossils from the 
Whitby Lias described by Stukely (1718) and by Chapman (1758) 
should be admitted among his wide group ‘‘les Crocopriss ;” and 
the doubt would be reasonable if the species so associated formed a 
series of only generic value. However, the Liassic fossils are 
admitted in the Crocodilian chapter of the ‘‘ Ossemens Fossiles,’ 
and their distinctive characters in relation to existing groups are 
pointed out with the author’s usual clearness. 
The Crocodilian remains from the later calcareous schists of 
Monheim, from the Oolitic stones of Caen, Havre and Honfleur, are 
described as kinds of “‘ Gavial’’$; those from the Weald of Sussex, 
we 
* “Tes vues les plus nouvelles perdent presque tout leur mérite quand 
elles sont dépourvues de cet appui.” ‘ Ossemens Fossiles,’ tom. v. pt. ii. p. 14: 
Ato, 1824. 
Tt “Un genre trés naturel.” I®d. ib. p. 20, 
+ *Crocopinia’ auctt.; Lorrcata, Merrem; Emyposaurta, Blainville. 
§ Of the vertebree of his ‘‘Gavial de Caen,” he expressly states, “ I] a ses 
deux faces trés-légérement concaves, et son milieu rétréci.” 
**C’est la, comme en voit, un caractére fort différent de celui des Crocodiles 
vivans, ou toutes les faces postérieures sont trés-convexes, et les antérieures 
trés-concayves.” Tom. cit. p. 137. 
