LIASSIC PLESIOSAURS. 15 



a length of four inches; the production, anterior to the transverse stem, being nearly 

 an inch in length. In the thirty -fifth vertebra (Tab. VII, c 35) the costal surface pro- 

 jects, the rib begins to ascend, the anterior production to shorten, the posterior one to 

 lengthen. In the thirty-seventh (ib., 37) the rib is supported in equal proportions by 

 the centrum and by a diapophysial growth of the neurapophysis. In the thirty - 

 eighth (c, 3S) the rib has passed almost wholly upon the diapophysis, and has assumed 

 a simple rib-like character, slightly bent, with a length of six inches. In the thirty- 

 ninth vertebra (ib., D 1) the transit from centrum to neurapophysis, np, is complete, 

 denoting the first of the dorsal series. In the second dorsal vertebra of the present 

 skeleton the rib has slipped forward from its joint, d. In the forty-third (Tab. V, 

 fig. 1) it is depressed an inch below the diapophysis. In the forty-sixth to the fiftieth 

 vertebree the heads of the ribs lie beneath the centrums, and the side view of the whole 

 of those vertebrae is obtained. In the succeeding dorsals the ribs gradually approxi- 

 mate their suspending processes, and have resumed their articulation at the twentieth 

 dorsal, or the fifty-eighth vertebra, counting from the atlas. 



The ribs of the forty-seventh to the fifty-first vertebrae are from sixteen to 

 seventeen inches in length ; they are the longest of the series. The articular head 

 presents a diameter of one inch and a half; the anterior surface is convex transversely; 

 the outer part of the posterior surface is rather concave in the same direction, so that 

 the outer margin of the proximal half of the rib, to near its head, presents the cha- 

 racter of an obtuse rim or ridge. They gradually decrease in size as the vertebrae 

 recede in position from the fiftieth ; and, at the sixtieth, are reduced to a length of 

 four inches : this and the two succeeding ribs seem to have become anchylosed to the 

 diapophyses. In the sixty-second vertebrae the rib suddenly augments in thickness, 

 extends its articulation downward upon the centrum, and represents a sacral vertebra 

 (Tab. I, s). That of the sixty-first vertebra is somewhat less thick, but it may have 

 assisted in affording attachments to the ilium (ib., 02), the proximal end of which 

 bone is in contiguity with the converging terminations of the ribs of the sixty-first 

 and sixty-second vertebrae. The anchylosed condition, with shortening of the caudal 

 ribs, or pleurapophyses, give them the usual chai'acter of transverse processes in 

 the caudal region. 



The neural spines, thin and antero-posteriorly extended in the neck (Tab. V, 

 fig. 2, a, 2, ns), have* been more or less broken away, in the operation of exposing the 

 specimen, from the anterior three fourths of the vertebra? in that region. Their height 

 gradually decreased as they approached the head and receded from that of the thirtieth 

 vertebra (ib., 30), which rises four inches from the summit to the neural arch, having 

 a fore-and-aft diameter of two inches three lines, and a thickness of three lines. 

 The former diameter is least a little above the origin of the spine, and gradually 

 increases toward the summit, where the spines are in contact. In the thirty-third 

 vertebra the neural spine is five inches in length, and its breadth of two inches three 



