AGATHAUMAS SYLVESTRIS. 107 



formed were inhabited by these huge monsters; that one of them lay down to die near the shore of probably a brackish- 

 water inlet, and was soon covered by the thickly fallen leaves of the wood; that continued subsidence of the level submerged 

 the bones, which were then covered with sand. 



The form of the ilium differs very materially from that of Hadrosaurus and the vertebra? are plane, thus differing from 

 Thespesius. The limb bone is distinct from anything in Lselaps, which, moreover, probably resembles Thegalosaurus in its 

 ilium. The present form recalls rather Cetiosaurus. As it is evidently new to our system, it may be called Agathaumas 

 sylvestris. 



In his Cretaceous Vertebrata Cope describes and figures the type in detail. His description 

 is as follows: a 



The characters of this genus are derived from the typical species A. sylvestris, which is represented by dorsal and lumbar 

 vertebrae and an entire sacrum, with the ilia, one nearly entire, ribs, and a number of other bones the characters of which 

 have not yet been positively ascertained. One of these resembles the proximal part of a pubis, others portions of the 

 sternum, etc. 



On eight (and perhaps nine) vertebra?, anterior to the sacrum, there is no indication of the capitular articular 

 facet for the rib. This facet is found, as in Crocodilia, at or near the base of the elongate diapophyses. The centra are slightly 

 concave posteriorly, and still less so on the anterior face, with gently convex margins. The neural canal is very small, and 

 the neural arch short and quite distinct from the centrum, having scarcely any suture. The neural arch has a subcubical 

 form, partly truncated above by the anterior zygapophyses. In like manner the base of the combined neural spine and 

 diapophyses are truncated below by the square-cut posterior zygapophyses. The diapophyses are long, and directed upward ; 

 they are triangular in section. 



There are eight (and perhaps nine) sacral vertebra?, which exhibit a considerable diminution in the diametei-s of the 

 centra. The diapophyses and neural arches are shared by two centra, the anterior part of a centrum bearing the larger por- 

 tion of both. The diapophyses are united distaUy in pairs, each pair inclosing a large foramen. The anterior is the most 

 massive and rests on the ilium; the posterior pair the most expanded; the superior margins of its posterior edge form an 

 open V, with the apex forward on the neural arch of the fifth vertebra. On the last sacrals the 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 ah but the last vertebra. 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 vertebra? as are found in the genus Hadrosaurus, and that the 

 tail was a less massive organ. 



The ilium is much more elongate than the corresponding element in Hadrosaurus, Cetiosaurus, 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 vertebra? was applied when in place. In front of this point the ilium is produced 

 in a straight line and a stout flattened form with obtuse end. Posterior to it its inner face is concave to receive the second 

 transverse rest of the sacruni, and the superior margin is produced horizontally toward the median line like the corresponding 

 bone in a bird. The posterior part of the bone is the widest, for it is expanded into a thin plate and produced to a consider- 

 able length. From one of the margins (my sketch, made on the ground, represents it as the upper) a cylindric rod is pro- 

 duced still farther backward. This it is believed is only the shaft of a displaced rib. The base of the ischium is coossified 

 with the ilium and is separated behind its base from 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 hones certainly referable to the limbs. 



The form of the ilia distinguishes this genus from those known heretofore. 



The last nine dorsal vertebra? have rather short centra, the most posterior 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 zygapophyses. 

 The neural spine is elevated and compressed, the diapophysis 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 vertebra? are flat- 

 tened 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 vertebra? are mere tuberosities. A large sutural surface for attachment of a transverse process is 

 seen on 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. 



Either 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 its plate presents a free margin on the outside as well as the inside of the femoral 

 articulation. 



a Pp. 53-56; also Bull. No. 2, U. S. Geol. and Geog. Surv. Terr., pp. 17-19. 



