560 
Mr. De la Beche and Mr. Conybeare on 
the head of this paper. The numerous important and illustrative 
specimens which he placed at my disposal, proved of material aid, 
and still more so his general acquaintance with the subject, of which 
I subsequently enjoyed the fullest advantage ; so that the facts now 
submitted to the Society must be considered as the fruit of inquiries 
prosecuted by us in common. 
A skeleton of the animal in question, deficient only in the bones 
of the head, preserved in the well known collection of Col. Birch, 
(who most liberally allowed us the full use of the very valuable 
materials he possessed)* confirmed in a most satisfactory manner 
most of my previous conjectures, and enabled us to assign to it its 
true place in the zoological order, and to designate it by an appro- 
priate name. That of Plesiosaurus has been chosen, as expressing 
its near approach to the order Lacerta. 
The points of analogy between the newly discovered animal and 
the Ichthyosaurus are sufficiently numerous and important to evince 
the propriety of their being referred to the same great natural family, 
a family on every account highly deserving an attentive examina- 
tion, its members being not only unknown in the recent state, but 
presenting many peculiarities of general structure, of which no other 
examples had been previously observed ; and of that most interest- 
ing description which affords intermediate forms, and as it were a 
transition between different races, and adds new links to the con- 
nected chain of organized beings. f 
* I have also to acknowledge our obligations on similar grounds to Mr. Bright, Dr. 
Dyer, Messrs. Miller, Johnson, Braikenridge, Cumberland, and Page of Bristol. 
+ When alluding to the regular gradation, and, as it were, the linked and concatenated 
series of animal forms, we would wish carefully to guard against the absurd and extrava- 
gant application which has sometimes been made of this notion. In the original formation 
of animated beings, the plan evidently to be traced throughout is this. That every place 
