7H) II. O. SEELEY ON THE VERTEBRAL COLUMN 



37. On the Vertebral Column and Pelvic Bones of Pliosaurus 

 Evansi (Seeley), from the Oxford Clay of St. Neotts, in the 



WOODWARDIAN MUSEUM of the UNIVERSITY of CAMBRIDGE. By 



Harry Goyier Seeley, F.L.S., Esq., F.G.S., &c, Professor of 

 Geography in King's College, London. (Read March 7, 1877.) 



Knowing how many Plesiosaurian genera have left their remains in 

 the great Pelolithic system formed by the Oxford Clay, Ampthill 

 Clay, and Kimmeridge Clay, and that triangular teeth have not been 

 obtained from the Oxford Clay of St. Neotts, some amount of indeci- 

 sion may be justifiable in the generic determination of this species. 

 Nevertheless the cervical and dorsal vertebrae closely resemble in 

 typical characters those of Pliosaurs from the Kimmeridge Clay ; and 

 I do not detect in them or in the pelvic bones indications of ap- 

 proximation to the known characters of any other genus. 



The remains are from the well-known pit in the lower part of the 

 Oxford Clay at Eynsbury, near St. Neotts, which yields Ammonites 

 Duncani, A. Lambert/, A. coronatus, &c. They comprise thirty-seven 

 vertebrae in sequence, of which twenty are cervical and about sixteen 

 dorsal ; and there is one pubic bone and one ischium. But the vertebral 

 bones were obtained at a former period, and the pelvic bones after 

 an interval of some years. We owe the discovery and preservation 

 of these fossils to J. J". Evans, Esq., of St. Neotts, who presented 

 them to the University of Cambridge : and it is in honour of the 

 discoverer that I propose the species should be named. 



The Atlas and Axis (figs. 1,2). 



These vertebra?, though in close contact, do not appear to have 

 been ankylosed together. They have lost their neural arches, like 

 all other Pliosaurian vertebrae. A large sub vertebral wedge -bone 

 beneath the atlas (e) projects forward to form the lower half of the 

 atlantal cup ; and behind this, so as to be continuous with it, was a 

 second subvertcbral wedge-bone, lost before fossilization, which 

 reached backward to within |- of an inch of the posterior border of 

 the axis. The extreme length of the two centrums along the neural 

 canal is Scinches, each Vertebra measuring about 1^ inch, while they 

 are parted by an interspace of g inch. The antero-postcrior extent 

 of the basal border to the margin of the anterior wedge-bone is 

 4 inches, of which the wedge-bone occupies 1| inch. This wedge- 

 bone has its anterior outline convex ; and its posterior margin, which 

 is subparallel, is gently concave. The extreme transverse measure- 

 ment of the bone is 2^ inches. Externally (that is, inferiorly) it is 

 convex from side to side, and slightly convex from front to back : it has 

 a small median posterior eminence, and a jn'ominence where it termi- 

 nates on each side. The superior or atlantal surface of the wedge- 



