R. Lydekker—Oxford and Kimeridge Clay Sauropterygia. 355 
propodials were described under the name of P. trochanterius. P. 
brachyspondylus was regarded as the Kimeridgian analogue of P. 
Oxoniensis ; the vertebre having the same short and distinctly cupped 
centra, which characterize both that species and P. Mansel. It should 
also be observed that Phillips described another large Kimeridgian 
Plesiosaur, which had flattened terminal faces to the centra, and is 
closely allied to P. plicatus, which belongs to a totally different sub- 
group. ‘Thus matters stood till 1874, when in vol. xxx. of the 
Q.J.G.S., Professor Seeley figured on p. 447 the above-mentioned 
pectoral girdle from Ely, under the new generic title of Colymbo- 
saurus ; stating on p. 445 that the type species was to be P. megadirus, 
which, as already stated, had never been sufficiently described. It 
was also mentioned on p. 448 that Plesiosaurus Manseli was to be 
referred to a subgenus of Murenosaurus. 
With these facts we may proceed to criticism. In the first place 
I cannot find any characters by which P. Manseli can be distinguished 
from P. trochanterius, and since the description of the latter is suffi- 
cient, I consider that we should adopt the earlier name. P. brachisto- 
spondylus appears, moreover, to be founded upon dorsal vertebrze of 
the same species which have been subjected to a strong crush in the 
axial direction. I have compared the vertebre figured by Phillips 
under the name of P. brachyspondylus, and also the types of his P. 
validus, with the corresponding vertebra of the column described by 
Mr. Hulke, and find an absolute identity between the two; the 
difference on which Phillips separated P. validus from P. brachyspon- 
dylus being merely due to the different serial position of the vertebre, 
and to an erroneous restoration of the neural arch. With regard to 
the type skeleton of P. megadirus, Prof. Hughes has been good enough 
to send some of the cervical vertebrae to London, and from coim- 
paring these, and from a personal examination of the rest of the 
skeleton two days after having carefully examined that of the so- 
called P. Manseli, I am fully and absolutely convinced of the specific 
identity of the two. This is also borne out by all the detached 
vertebre of this type from the Cambridgeshire district in the British 
Museum, which cannot be distinguished from those of the latter. 
Further evidence is afforded by the above-mentioned paddle in the 
Cambridge Museum, and by another in the collection of Mr. Fisher, 
in both of which the propodial is of the P. trochanterius type. 
Now comes the question of the pectoral girdle on which Colymbo- 
saurus was founded. As this was referred definitely by its describer 
to the so-called P. megadirus, 1 had imagined that it was associated 
with vertebree of the same type as those of the latter; but my 
astonishment on arriving at Ely was considerable on hearing from 
Mr. Fisher that it was an entirely isolated specimen. Although I 
think it most probable that this specimen is referable to the present 
form—that is, P. trochanterius—yet Prof. Seeley, on the supposition 
that these two forms were distinct, had no more grounds for referring 
it to P. megadirus rather than to P. Manseli, unless he assumed that 
all the Cambridgeshire specimens belonged to the former and all the 
Dorsetshire to the latter. Even then, however, there was also the 
