AGATHAUMAS SYLVESTEIS. 109 



"by Cope, as is also the fragmentary coossified neural arch shown by him in PL IV, fig. 18, of 

 his Cretaceous Vertebrata. The undetermined bones shown by him in PI. IV, figs. 19, 19a, 

 and 2d, are also present. No pelvic bones, other than the ilium mentioned above, and no limb 

 bones pertaining to the type are to be found, and since they have nowhere been described by 

 Cope it is doubtful whether they were ever recovered except, perhaps, in an extremely frag- 

 mentary and hopeless condition. 



DETAILED DESCRIPTION. 



The ilium. — This, after the sacrum, is the most important element of the original type. 

 The right ilium is present and complete save the anterior and posterior extremities and a 

 portion of the pubic peduncle, which are wanting. 



The blade of the ilium is much extended, both anterior and posterior to the acetabulum. 

 The anterior extremity appears broad and somewhat truncated when compared with the pointed, 

 narrow, and elongate posterior extremity. When adjusted to the sacrum the expanded blade 

 of the ilium is more nearly horizontal than vertical, just the opposite from that which obtains in 

 the sauropod dinosaurs and more closely resembling that of the Mammalia. In this position the 

 external edge, when viewed from above, presents a compound curve, gently concave ante- 

 riorly and more decidedly convex throughout the posterior two-thirds of its length. When 

 viewed from in front the external border continues in the same horizontal plane until just 

 above and a little posterior to the ischiac peduncle, when it bends abruptly downward. This, 

 the external margin, is moderately thick throughout its entire length, but it is greatly thickened 

 near the posterior and anterior extremities and in the deflected region just above the ischiac 

 peduncle. The broad superior surface of the ilium is convex transversely throughout its 

 middle region, but concave at either extremity; antero-posteriorly it is gently convex through- 

 out its entire length. The internal margin is rather thin at either extremity, but considerably 

 thickened and otherwise modified medially for contact with the sacrum. The inferior surface 

 of the ilium gives origin to the ischiac and pubic peduncles, which spring from near its internal 

 margin. From the base of the pubic peduncle a broadly convex ridge of bone extends diago- 

 nally across the anterior blade of the ilium to its antero-external angle, inclosing in front the 

 deep concavity which occupies the inferior surface of this bone just external to the acetabulum. 

 The inferior surface of the posterior blade is a nearly fiat surface. The ischiac peduncle is 

 low, broad, and much expanded both transversely and antero-posteriorly. The articular sur- 

 face of the pubic peduncle is wanting; that portion of the base remaining indicates, however, 

 that this element, although more slender, was actually longer than the. ischiac peduncle. In 

 the Ceratopsia the ilia are never coossified with the sacrum, and in the present specimen the 

 surface for attachment with the sacrum is but poorly indicated. In Cope's description of this 

 ilium he mistook the anterior for the posterior extremity, erroneously described the base of 

 the ischium as coossified with the ilium, and stated that there was no facet for the pubis. 

 Some of these errors he corrected after the descriptions of more complete material by Professor 

 Marsh. 



The vertebrie. — The nine posterior dorsals figured by Cope are all accessible. These, save 

 the second from the first of the series, are represented only by the centra, for the most part in 

 a much damaged condition. The exact association of the detached neural arches mentioned 

 above is uncertain. With the second, held in place by the surrounding matrix, there is the 

 neural arch, but without the spine or transverse processes. This arch, as well as those of the 

 other vertebra? represented in the series, were united only by suture with their respective centra, 

 thus indicating that the individual had not yet reached maturity. All the dorsal centra are 

 short, deeper than broad, plano-concave or slightly biconcave, constricted medially and obovate 

 in cross section. The neural canal is small, its vertical diameter exceeding the transverse, 

 and is nearby inclosed by the neural arches, but inferiorly it is bounded by the superior surfaces 

 of the centra. The neural arch is rather high, rising about 85 mm. above the neural canal 

 before giving origin to the- transverse processes. Of the detached neural arches, each bearing 

 a transverse process, mentioned above as still associated with the type material, one has been 



