AND SAFROPTERYGIANS OF THE PnEDECK ETC. 51 



appears impossible by the teeth alone to distinguish this Pliosaur 

 from P. f'erox. 



Of the cervical vertebrse a centrum, with the cervicalribs, from the 

 hinder region of the neck, is represented of three fourths the natural 

 size in PL V. fig. 2. This vertebra presents all the characters of a 

 typical Pliosaur. Its terminal faces are subcylindrical, and have 

 no marailla round the central depression ; the costal facets are 

 very prominent ; and the external surface is highly rugose. The 

 dimensions are : length 1-75, height 3*6, and width 4*0 inches. The 

 length is therefore very nearly half the vertical diameter. A rather 

 later cervical, in which the terminal faces have become transversely 

 ellipsoidal, has a height of 3' 7 and a width of 4-3 inches, the true 

 length not being determiuable owing to crushing. The neural arch 

 represented in PL Y. fig. 3 shows the presence of large and well- 

 developed zygapophyses. Unfortunately the nature of the cervical 

 zygapophyses in the Kimeridgian Pliosaurs does not appear to be 

 known. In the dorsal region, however, the zygapophyses were of 

 very small size and almost aborted in the Pliosaurs of the 

 Kimeridge Clay ; and an immature vertebra in the Eyebury collection 

 shows that the same condition obtained in at least one of the 

 Pliosaurs of the Oxford Clay. There are no signs of any sutural 

 connexion of the arches and ribs with the centra of the cervical 

 vertebrae in the specimens uuder consideration. 



If my memory does not fail me, these cervicals closely resemble 

 an associated series in the Cambridge Museum from the Oxford 

 Clay of Great Gransden, near St. Neots, Huntingdonshire, to the 

 owner of which Prof. Seeley has applied the name of Pliosaurus 

 pachijdirus, although without any description to justify the adoption 

 of that name *, these specimens being noticeable for the prominence 

 of the costal articulations. The form to which that name was 

 applied I have provisionally included in the work cited in P. fero.v. 

 On p. 146 of that work an imperfect late cervical vertebra 

 (No. 47429) from the Oxford Clay near Peterborough is provision- 

 ally referred to the same species. On comparison with the present 

 specimens such a marked resemblance is presented by that vertchra, 

 that there seems to be every reason for considering both as specifically 

 the same. It is true, indeed, that in the Pritish-Museum vertebra 

 the costal facets are less prominent than in Mr. Leeds's specimens ; 

 but I think this difference may be partly due to individual 

 variation, and partly to the edges of these facets in the former 

 specimen having been chipped. 



That the vertebra? under consideration indicate a totall}'- difFerent 

 form from the one to which the name of Pliosaurus Evansi has been 

 applied, is quite evident f. Thus the typical cervical vertebra} of 

 the latter (which through the courtesy of Prof. Hughes I have been 

 enabled to compare with the s])ecimens under consideration) difi'er 

 not only in their much smaller size, but in their proportionately 

 greater length, which much exceeds half the vertical diameter of 



* See ' Catalogue ' op. ci^. p, 145. 

 t See 'Catalogue,' p. 128. 



e2 



