20 
ON A PYRITIOUS CONCRETION FROM TEE LIAS 
of Whitby , which appears to show the external form of the 
body of embryo's of a species of Plesiosaurus. 
By H. Gk Seeley, F.R.S 
In 1887 I received a fossil from J. F. Walker, Esq., M.A , 
F.GkS., which he had obtained from a dealer at Whitby. It 
appeared at first to be mineralized with phosphate of lime, but 
has since proved to consist of iron pyrites, which has obliterated 
whatever evidence there may have been of internal structure. 
Upon the surface of the concretion are several elongated forms 
in high relief, almost as well rounded and well defined as 
though they were artificially modelled, which I regarded as 
embryos of a Plesiosaurus. As such the specimen was exhibited 
and briefly described at the meeting of the British Association 
in 1887, at Manchester—Report, page 697. I am still unable 
to interpret the specimen in any other way ; it therefore seems 
desirable to record its essential characters. 
The specimen is a central concretionary mass of compact iron 
pyrites with mierocrystalline texture. The surface of this iron 
pyrites was covered, and is in part still covered, with a smooth 
film of hard clay. This film has much the aspect of a 
defining membrane of a placenta-like character, upon which the 
embryos are clustered and elevated, so as to exhibit curved 
forms of well-rounded bodies, which correspond to the main 
contours of the concretion, above which they are for the most 
part prominently elevated. There are four principal masses, 
each of which may be regarded as an embryonic plesiosaur ; 
and in addition to these there are indications of three or four 
others. They partly overlap each other, are in various stages 
of preservation and of development, and are chiefly interesting 
for showing the external form of the body as it may be presumed 
to have been at the time when the parent animal died 
There are many examples of preservation, for a time at least, 
of the soft parts of animals in various geological deposits. The 
Solenhofen slate has yielded specimens which demonstrate the 
forms and structures of Pterodactyle’s wings, of bird’s feathers, 
of jelly-fish, and cuttle-fish. These remains prove that there is 
no a priori improbability of the external form of the soft parts 
