R. Lydekker—Oxford and Kimeridge Clay Sauropterygia. 3538 
be closely allied to Thawmatosaurus oolithicus, of the Lower Jurassic 
of Wiirtemberg, in which the teeth have the same structure and the 
cervical vertebree are likewise furnished with two costal facets. The 
latter species, again, appears to come so close to the Upper Liassic 
Plesiosaurus Cramptoni—the type of Prof. Seeley’s genus Rhomaleo- 
saurus—-that with our present material not even specific characters 
can be recognized. On these grounds I am inclined to include all 
these three species, together with the Lower Liassic P. megacephalus, 
in a single genus, for which the name Thaumatosaurus should be 
adopted. This reference J shall again have occasion to mention in an 
addendum to a paper on the Oxfordian species in the ‘“ Geological 
Society’s Journal”; the knowledge J have gained since that paper 
was read having induced me to remove that species from the genus 
Plesiosaurus. Mr. Leeds’ examples show that a small omosternum 
was present. 
Of the genus Pliosaurus Mr. Leeds possesses only a number of 
detached teeth, which differ from those of the Kimeridgian forms in 
the imperfect development of the “carine,” and the absence of the 
distinct smooth and flat intercarinal space. These teeth appear 
indistinguishable from the one from the Oxfordian of Boulogne 
described and figured by M. Sauvage under the name of Liopleurodon 
feroz. I can see, however, no reason why this species should be 
separated from the Owenian genus, and it may accordingly be known 
as Pliosaurus ferow. 'The cervical vertebrae from the Oxford Clay in 
the Cambridge Museum to which Prof. Seeley has applied the name 
P. pachydirus, without, however, giving any specific diagnosis, are 
probably referable to the same species. 
Leaving now the Eyebury Collection with the expression of my 
thanks to its owner for his courtesy in placing it thus freely before 
me, our attention may be directed in the remaining part of this paper 
to certain large Plesiosaurian remains from the Kimeridge Clay, 
which are allied to P. Oxoniensis. In the first place I may mention 
that after leaving Peterborough I availed myself of the permission 
of Mr. Marshall Fisher, of Ely, to visit his collection, which contains 
the pectoral girdle figured by Prof. Seeley on p. 447 of the thirtieth 
volume of the “ Geological Society’s Journal,” under the name of 
Colymbosaurus, and thence proceeded to the Woodwardian Museum 
at Cambridge to have one more look at the vertebral column to which 
the same authority has given the name of Plesiosaurus megadirus ; 
both specimens being from the Kimeridge Clay of the Cambridge- 
shire district. 
Before going further it is, however, necessary to recapitulate briefly 
the history of these large Kimeridgian Plesiosaurs. In the “ British 
Association Report ” for 1839, Sir R. Owen described a propodial 
bone (humerus or femur) of a large Plesiosaur from the Kimeridge 
Clay of Shotover in the collection of the late Lord Enniskillen, under 
the name of Plesiosaurus trochanterius ; this specimen being now in 
the British Museum. Its structure is shown in the accompanying 
woodcut of anotherexample. In the year 1841 this species, together 
with P. grandis, was referred to the genus Pliosaurus; of which the 
DECADE III.—VOL. V.—NO. VIII. 23 
