Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/637

Rh of the base of the centrum external to the ribs is 2$7⁄8$ inches. The bases of the ribs are strong, elevated, and directed chiefly downward. The sides of the centrum are smooth, concave from front to back, and moderately convex from above downward, and extend vertically for 1 inch above the ribs; the neural arch is confluent with the centrum, and unites with it by a large compressed squamose base, which fits into an impressed concave area.

The fourth specimen is 3$3⁄4$ inches long; and the whole centrum is somewhat larger, with flatter articular faces and deeper excavations on the base of the centrum. The fifth, a trifle longer, shows the neural canal as a deep channel, concave from front to back, and at least an inch wide. The articulation for the rib is nearer towards the anterior margin of the centrum, where the process is thicker than posteriorly; as fractured it is 1$7⁄8$ inch long. The seventh centrum is 4 inches deep and about $1⁄4$ inch wider; so that the articular face has become morecircular. This surface is much flatter, but now has a shallow central concavity an inch in diameter. The centrum is 4$1⁄2$ inches long; its basal excavations are more elongated, and the upper part of the centrum is more compressed. The eighth centrum is larger in the articular faces. The neurapophyses are remarkably extended from front to back, and greatly compressed, each being less than $1⁄4$ inch thick. On the base, separated by the rounded median ridge, are two large oval nutritive foramina about $3⁄4$ inch apart. The bases of the ribs grow stronger and are $7⁄8$ inch in depth. The tenth centrum is 4$1⁄4$ inches long, with the articular face as deep and 5$1⁄8$ inches wide, though the width over the articulations for the ribs is somewhat less. In the eleventh the base for the rib has become more ovate and larger, and the base of the neural canal has increased with the size of the vertebra, the neural arch being 2 inches wide externally behind.

The thirteenth vertebra has the neural arch well preserved (Pl. XXIII. fig. 2). The centrum is 4 inches in antero-posterior length. Its anterior face is 5$3⁄4$ inches wide and about 4$1⁄2$ inches deep. It has a central depression 2 inches broad, margined by an elevated rounded rim, between which and the circumference is a second concave area in the form of a ring, but less deep. The posterior articulation is 6 inches broad and 4$1⁄2$ inches deep; it has the transversely oval central area shallow, but without the elevated rim. The base of the centrum is 4$1⁄4$ inches long; it is convex from side to side, with an obtuse median ridge. The distance between the articulations for the ribs is 5$1⁄4$ inches. The articular surface for the rib is subcircular, l$3⁄4$ inch deep, and near]y 1$1⁄2$ inch from front to back; this area is $3⁄4$ inch from the posterior margin and more than 1$1⁄2$ inch from the anterior margin of the centrum. The lateral area above the articulation for the rib is flattened, concave from side to side, and scarcely concave in depth. And the neural arch rises steadily from the side of the centrum without any break to a height of 10$1⁄2$ inches, being imperfect superiorly. The neural arch is much compressed from side to side. The posterior zygapophyses hang entirely behind the posterior articular face of the centrum ; they are close together, being