18 



bearing tlie larger portion of both. The diapoph yses are united distally 

 in pairs, each pair inclosing a large foramen. The anterior is the most 

 massive rest on -the ilium ; the jjosterior pair the most expanded ; the 

 superior margins of its posterior edge form an open Y with the apex for- 

 ward on the neural arch of the fifth vertebra. On the last sacrals tlie 

 diapophyses rise to the neural arch again. The exits of the sacral spinal 

 nerves are behind the middles of the centra, and continue into grooves 

 of the sides in all but the last vertebrae. The reduced and rather elongate 

 form of the last sacral vertebra induces me to believe that this animal 

 did not possess such large and short caudal vertebrae as is found in the 

 genus JETadrosmirus, and that the tail was a less massive organ. 



The ilium is much more elongate than the corresponding element in 

 Sadrosaurus, Cetiesaurits, or Megalosaurus. Its upper edge is turned and 

 thickened inward above the anterior margin of the acetabulum, and here 

 the middle of the conjoined diapophyses of the second and third sacral 

 vertebrae were applied when in place. In front of this point the ilium is 

 produced in a straight line, in a stout, flattened form with obtuse end. 

 Posterior to it its inner face is concave, to receive the second transverse 

 rest of the sacrum, and the superior margin is produced horizontally 

 toward the median line like the corresponding bone in a bird. The pos- 

 terior part of the bone is the widest, for it is expanded into a thin plate 

 and produced to a considerable length. From one of the margins (my 

 sketch made on the ground represents it as the upper) a cylindric rod is 

 produced still further backward. The base of the ischium is co-ossified 

 with the ilium, and is separated fi^om the iliac portion of the acetabulum. 

 There is no facet nor suture for the pubis at the front of the acetabulum. 



The ribs are compressed. There are no bones certainly referable to the 

 limbs. 



The form of the ilia distinguishes this genus from those known here- 

 tofore. It is also highly probable that it differs from some other genera 

 in which the ilium is not known, e. g., Thespesius, in the smaller and 

 differently formed tail. 

 AaATHATJMAS SYLVESTRis, Copc. Proceed American Philos. Soc, 



1872, 482. 



The last nine dorsal vertebrae have rather short centra, the most pos- 

 terior the shortest. They are higher than wide; the sides are concave, 

 the inferior face somewhat flattened. The neural arch is keeled behind 

 from the canal to between the posterior zygapophyses, and a similar keel 

 extends from the base of the neural spine to between the anterior zyga- 

 pophyses. The neural spine is elevated, broad, and compressed ; the dia- 

 pophysis is convex above and concave along the two inferior faces, most 

 so on the posterior. The articular face of the first sacral vertebra is wider 

 than deep. The eight sacral vertebrae are flattened below, in all except 

 the first by a plane which is separated from the sides by a longitudinal 

 angle. The neural spines of the anterior five sacral vertebrae are mere 

 tuberosities. A large sutural surface for attachment of a transverse 

 process is seen in the posterior third of the eighth sacral vertebra, 

 which descends nearly as low as the plane of the inferior surface. On 

 the tenth sacral there is no such process, but its neural arch and that of 

 the ninth support transverse processes. These are more like those of 

 the dorsals in having three strong basal supporting ribs, the anterior 

 and posterior extending for some distance along the arch. 



Whether naturally or in consequence of distortion, the plate of the 

 ilium is at a strong angle to the vertical axis of the acetabulum, and at 

 the posterior part of it, the margin of the plate is free on the outside as 

 well as the inside of the femoral articulation. 



