Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/638

544 separated by a vertical slit. The processes are imperfect; as preserved each is 1$1⁄2$ inch long and fully $7⁄8$ inch wide. These oblong facets look downward and slightly outward. The neurapophyses are greatly compressed from side to side. The neural spine is more compressed in front than behind, the base of its posterior margin is parallel to the posterior face of the centrum; it hangs backward, and measures in the upper part $3⁄4$ inch in width. The external width of the neural arch in its middle is 1$3⁄4$ inch.

Fourteenth to seventeenth—as the articular tubercle for the rib begins to ascend the side of the centrum the tubercle becomes a little prolonged and is rounded. The eighteenth vertebra (Pl. XXIII. fig. 3) has the base of the neural arch preserved; its compressed anterior margin is nearly flush with the anterior face of the centrum, but as it ascends it extends forward. The face of the centrum is 6$5⁄8$ inches wide. The articular facets for the ribs are nearly on the middle of the sides of the centrum; and the base accordingly becomes more rounded from side to side, and is nearly flat from front to back. The tubercle for the rib now steadily ascends the side of the centrum, leaving the base perfectly rounded. The nineteenth has the centrum 4 inches long at the base and 3$1⁄2$ inches long superiorly (Pl. XXIII. fig. 4). The articular surface is more than usually flattened, 6 inches broad, and 4$1⁄2$ inches deep. The transverse process was deep and narrow, placed posteriorly, and formed mainly by a downward and backward prolongation of the neural arch. This shows that the true neck is ended, the vertebra belonging to the two or three which form a transition between the cervical and dorsal series, which are conveniently named pectoral. The twentieth and twenty-first show similar characters; only the transverse process increases in size and depth, and rises higher.

Several of the dorsal vertebræ are so similar that one maybe taken as a type (Pl. XXIII. fig. 5). It is well preserved, except that the neural spine is broken away. The centrum measures 4$3⁄8$ inches in length along the visceral surface from back to front; but in the line of the neural canal it only measures a little over 3 inches. Under the neural canal the articular face is 5$1⁄8$ inches deep, and as preserved is 5$1⁄2$ inches wide in the middle. The vascular perforations on the base of the centrum are 1$3⁄4$ inch apart; the bone between them is remarkably convex. Below the neural arch the sides of the centrum converge greatly, measuring less than 3 inches transversely. The arch shows the vertically ovate neural canal; the base of the neural spine is narrow, compressed, and directed backward; and the broken transverse processes are directed outward and upward. The height from the base of the centrum to the shoulder of the transverse process is 7$1⁄2$ inches. The transverse processes are compressed from front to back, about 2 inches deep at their origin, and 1 inch wide; they are twisted so that the superior margin is inclined forward and the inferior margin inclined backward. The whole neural arch is a good deal compressed from back to front. The later dorsal vertebræ are slightly shorter, and the articular face of the centrum becomes