VERTEBRAL CHARACTERS OF PLESIOSUCHUS. 159 
extending to the outer nostril; jaws long, slender, with numerous 
small, sharp-pointed teeth (fig. 3, 1). 
Genus Plestosuchus, Owen. Vertebre platycclian; nasals extending 
to the outer nostril ; j aws short, stout, with few large teeth (fig. 3, 2). 
(The terms “ numerous” and “small,” “few” and “large ” relate 
to the Crocodilian series.) 
In connexion with the annectant or transitional characters of 
Plesiosuchus, already referred to, I may finally remark, that the 
gist of Geoffroy’s ‘ Mémoires’ of both 1825 and 1830 was to inter- 
pret the Cuvierian facts according to the Lamarckian ‘ Hvolutional 
Hypothesis of Species’ with modification of its dynamics. This 
hypothesis Geoffroy adopts in the following terms :—‘ La formation 
successive et leur évolution dans le cours des ages.” He then pro- 
ceeds :—‘ Je montrerai des formes remplacées insensiblement par 
d’autres, quin’auraient pu s’accommoder de l’ancien ordre des choses; ” 
in other words the “ battle of life” was against them. 
Reflecting on the paleontologist who guided his course in science 
“nar de farts positifs,’ Geoffroy affirms ‘‘qwil renonce 4 ce qwil 
y a de plus vif, de plus enivrant, et de plus philosophique dans la 
vie des sciences.” Les modifications insensibles d’un sidécle 4 un 
autre finissent par s’ajouter et se réunissent en une somme quel- 
conque. Si ces modifications amenent des effets nuisibles, les 
animaux qui les éprouvent cessent d’exister, pour étre remplacés 
par d’autres, avec des formes un peu changées, et changées a la 
conyenance des circonstances”*. Geoffroy’s fourth Mémoire is en- 
titled “Le degré @influence du monde ambiant pour modifier les 
formes animales.” 
Under this conviction Geoffroy rejoiced to see the transitional step, 
though short, which the extinct Oolitic Crocodile of Quilly, his 
Stencosaurus, made towards the modern Gharrial. Still more exultant 
would have been his reception of the form here described of an 
advance, in a Secondary formation nearer our times, beyond the long 
and slender-beaked primitive Mesozoic forms to the shorter and 
broader cranial organization of the widely distributed Crocodilia 
represented by the existing genera of that order of Reptiles. 
Discussion. 
The Prestpent said that both he and E. Deslongschamps had 
arrived at the same conclusions as those announced by Sir Richard 
Owen as to the Crocodilian affinities of the Kimmeridgian fossils. The 
greatest confusion had arisen with regard to the genus Steneosaurus. 
He found that the Kimmeridge fossil agreed in certain respects with 
the definition of the genus by Geoffroy, and he thought it preferable 
to employ the old name rather than to invent a new one. 
The AvrHor said that in the Oolitic Crocodiles the vertebre are 
amphiccelian, in the Tertiary ones they are united by ball and sockets ; 
in an intervening formation proportions of the modern crocodilian 
skull are combined with amphiccelian vertebre. The discovery of 
a form intermediate in age and transitional in form between Stenco- 
saurus and Crocodilus had an interesting bearing on Geoffroy’s often 
expressed views on evolution. 
* Loc. cit. 4eme Mémoire, p. 79. 
