344 Transactions. — Geology. 



in specimen 3 c, the length of the centrum is 2 inches, while the transverse and 

 vertical diameter are 3 inches and 2 -3 inches respectively. In specimen 3 c? a 

 posterior dorsal vertebra, without the neural spine, is recognized as belonging 

 to this species, by the transversely elongated tubercle and the character of the 

 articular facet. One end of the centrum has been broken off, so that its 

 length cannot be ascertained, but it measures transversely 4 inches, and 

 vertically 3 '3 inches. The lateral processes spring from the side of the 

 centrum, and not from the inferior third, as in the cervical vertebrae ; and 

 the neural spine, though broken off, has been distinctly continuous without 

 any suture. This fusion of the neural arch, both in the anterior and posterior 

 parts of the column thus indicated, confirms the suspicion that this species 

 should be placed in a genus distinct from Flesiosaurus. On the same slab 

 with this vertebra are thirty-two phalanges, exposed in their natural position 

 in continuous rows ; the largest about 2-7 inches in length, cylindrical, and 

 only moderately constricted at the middle. 



4. Plesiosaurus holmesii, n. sp. 



This species is allied to P. hoodii, in the trigonal form of the vertebral 

 centrum and the strong wedge-shaped neural spine continuous with the body 

 of the vertebrae. They are, however, at once distinguished by their flat, 

 smooth, articular surfaces, and the absence of the elongated tubercle in the 

 centre. Eleven posterior cervical vertebrae (4 a) have a length in sitH of 2 feet. 

 They were found on the exposed surface of a slab, and are therefore water- 

 worn, so that their transverse dimensions obtained are not trustworthy, but they 

 appear to have been about 3 inches in diameter. In the same slab is a fragment 

 of a shaft of a humerus, and the margin of a coracoid (4 6, c), with a scapulo- 

 humeral articulation, which seems to have resembled closely that of Mauisaurus. 

 The proximal end of a humerus (4 d), found by Mr. McKay at the Amuri Bluff, 

 has been referred to this species on account of associated vertebral fragments. 

 The articular head of the bone is peculiar, being divided into two portions by 

 a bicipital notch, not a groove, as in Mauisaurus. The external part of the 

 facet is a square, flat-topped, trochantei'-like process, but continuous with the 

 curve of the inner portion, which is nearly circular, convex, and deeply pitted, 

 in the manner of Plesiosaurus. It is not improbable that both this and the 

 last-mentioned species should be referred to Professor Owen's genus of 

 Pleiosaurus. 



0. Plesiosaurus traversii, n. sp. 



This is a very marked species, easily distinguished by the large quadrate 

 centra of the vertebrae, that always show a tendency to split into four parts in 

 the line of the venous foramina, and a constriction of the lateral border. 



No. 5 a. — Nine cervical vertebrae, much water-worn, but showing the 



