and the width 30 in. Its vertebrae are flat below, with latero-inferior 

 angles. The last centrum gives off a simple diapophysis. 



Another vertebra exhibits a diapophysis as low as the floor of the neural 

 canal and united by coarse suture. Others posterior to the sacrum are 

 more elongate with slightly compressed centrum, and with diapophysis 

 opposite floor of canal and not united by suture. Centra flat below ; no 

 chevron bones discoverable. Length centrum, 4 in. 4 lines ; depth of 

 articular face, 4 in.; width of do. 4 in. 3 lines. . 



The iliac bone is extended antero-posteriorly. One extremity is thick 

 and rather obtuse, but of little depth. There is a large protuberance 

 above the acetabular sinus. The other extremity is dilated into a flat 

 thin plate of rather greater length than the stouter extremity. From 

 one of its margins, a rod-like element projects. Its total length is about 

 four feet, of which the acetabular sinus measures about 8.10 inches. 



A short bone pertaining to the limbs has the articular surfaces at a 

 strong angle to each other, hence the shaft is twisted. It is deeply 

 grooved on one side near the extremity. The other extremity bears a 

 rather flattened hour-glass shaped articular face, and below it on one 

 angle is a crest. The convexity of the surface is not great, and this 

 extremity resembles that of a Dinosaurian or Crocodilian reptile. Its 

 length is, however, only eight and a quarter inches ; apparently too small 

 for a humerus, though this is not certain, while it is decidedly too small 

 for a metatarsal of such an animal. 



From the above description, it is evident that the animal of Black 

 Buttes is a Dinosauran reptile, the characters of the sacral and iliac 

 bones alone sufficing to demonstrate this point. If the reader will 

 compare the measurements given for species of this group already known, 

 he will observe that those of the present animal exceed those yet described 

 from North America. It is possible that if the corresponding parts of 

 Iladrosaurus tripos, Cope, or Thespesius occidentcdis, Leidy, are dis- 

 covered, they may approach it. 



It is thus conclusively proven that the coal strata of the Bitter 

 Creek Basin of Wyoming Territory, which embraces the greater area 

 yet discovered, were deposited during the Cretaceous period, and not 

 during the Tertiary, though not long preceding the latter. It ap- 

 pears that the forests that intervened between the swamps of epochs, 

 during which the coal was formed, were inhabited by these huge mon- 

 sters. That one of them laid down to die near the shores 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 by sand. 



The form of the ilium differs very materially from that of Iladrosau- 

 rus, and the vertebrae are plane, thus differing from Thespesias. The 

 limb bone is distinct from anything in Lmlaps, which, moreover, probably 

 resembles Thegalosaurus in its ilium. The present form recalls rather 

 Cctiosaurus. As it is evidently new to our system, it may be called 

 Agatiiatjmas sylvestris. 



