110 THE CEKATOPSIA. 



referred by Cope to the eighth and another to the ninth of the series. These transverse proc- 

 esses are triangular in cross section and bear, near their union with the neural arches, capitular 

 rib facets, while the one best preserved shows at its extremity a portion of the tubercular rib 

 facet. The capitular facets are each supported inferiorly by a single strong vertical lamina or 

 buttress, which springs from the posterior lateral border of the neural arch. The zygapophyses 

 on either side are placed very close together, both anterior and posterior, those of one side 

 being separated from those of the other by a very narrow median ridge or keel. The articular 

 surface of each occupies a single horizontal plane, the anterior looking upward, the posterior 

 downward. The remarkable simplicity exhibited in the articulation of these vertebrae con- 

 trasts strongly with the complicated condition which obtains in the same region of the verte- 

 bral column of the Sauropoda. I can not understand Cope's reason for describing the neural 

 arch as "short and with scarcely any suture," save that he meant antero-posteriorly. 



The sacrum. — The sacrum as figured and described by Cope is in a fair state of preserva- 

 tion. The three sacro-caudals figured by him as Nos. 15, 16, 17 of the vertebral series are 

 evidently posterior sacrals or sacro-caudals and represent 7, 8, and 10 of the functional sacrals, 

 1 and 9 being wanting, not having been preserved. In one of these the neural arch is preserved, 

 but in the other two only the centra remain, though fortunately in a better state of preserva- 

 tion than are those of the dorsal region. They are somewhat more elongate than the dorsal 

 centra and have the vertical and transverse diameters more nearly equal. The inferior surface 

 of each is broad and slightly concave. Superiorly they expand laterally at either extremity in 

 order to give support to transverse processes, which, however, are wanting in the present 

 specimens. These centra are not so regularly constricted medially as are those of the dorsals, 

 and this is especially true of that centrum numbered 17 in Professor Cope's figures. The 

 neural arch is compressed and low when compared with that of the dorsals. The two coos- 

 sified neural arches referred to and figured by Cope as sacrals are present and appear to have 

 occupied a position in the vertebral column similar to that shown in Cope's figure. I believe 

 they pertain to two of the posterior sacrals or sacro-caudals. 



The five true sacrals are present and decrease regularly in size from the first to the last, 

 as shown in PI. XXV. The centra of the first and second of these vertebras are comparatively 

 broad and short; those of the three posterior are more elongate. All the sacral ribs or trans- 

 verse processes spring more directly from the union of the centra in the present sacrum than 

 in that of Triceratops , as will be seen from a comparison of the figures, a condition apparently 

 somewhat intermediate between that which obtains in Monoclonius and Triceratops. In the 

 latter genus, as has already been pointed out, only the anterior of the sacral ribs takes its origin 

 about equally from two vertebras, the three posterior pairs of sacral ribs taking their origin 

 almost entirely from the anterior half of a single centrum. The sacral ribs are strong and 

 they unite distally to form a strong bar, which articulates with the ilium and forms a portion 

 of the acetabular wall. Together the four sacral ribs inclose three large foramina. It would 

 perhaps be better to consider only the four posterior of these vertebrae as true sacrals and 

 treat the anterior as a sacro-lumbar. It is probable also that had the animal been fully adult 

 there would have been attached to this still another sacro-lumbar, as in the sacrum of Tricera- 

 tops. The total number of vertebrae united in the sacrum would then be 10, as in the last- 

 mentioned genus. There are represented in the type 18 instead of 16 vertebrae, as stated by 

 Cope, and his figures show 17 centra and portions of 18 vertebrae. 



The undetermined bone shown by Cope in figs. 19 and 19a, PI. IV, of his Cretaceous Verte- 

 brata I believe to be a lateral metapodial, though somewhat crushed and distorted. 



The ribs. — Only portions of two ribs pertaining to the type specimen are to be found. 

 One of these consists of a fragment about a foot long, representing the proximal portion of a 

 rib from the mid-dorsal region, with both the head and tubercle wanting. It is much flattened 

 proximally, but becomes triangular in cross section beyond the tubercle. The other rib is 

 nearly complete and is from the posterior region, though not the last of the series. The head 

 and extreme distal end are both wanting. It is flattened proximally, becoming subovate 

 beyond the tuberculum and subelliptical toward the distal extremity. 



