NO. lece. OSTEOLOGY OF OAMPTOSAURUS—aiLMORLl. 299 



In comparing the conditions here with the sections so carefully 

 worked out by Dr. F. B. Loomis" at Como Bluif and Little Medi- 

 cine, in an area a few miles to the west of that under discussion, 

 it appears that this sandy layer may be tentatively correlated with 

 No. 28 of his section (see Plate 20), which he describes as follows: 



No. 2S is a gi'ay sandstoue iu wbicli the rich Bone Cabin Quarry is situated, 

 and also tlie Stegosaurus Quarry. The sandstone varies extremely in hard- 

 ness, being, iu the south part of Bone Cabin Quarry, soft and mixed with con- 

 siderable clay so that it is workable with an awl. In the northern part of the 

 quarry, however, there are bands of the firmest sort of sandstone. In Como 

 Bluff the layer is clay with merely an admixture of sand. Bone Cabin Quarry 

 has yielded a great variety of genera : Diplodociis, Morosaurus, Brontosaurus, 

 AUosaiinis, Ccratosaurus, Camptosaurus, Stegosaurus, as well as several 

 genera of carnivorous Dinosaurs; also Cnmpscmys and Goniopholis. 



The correctness of the above correlation appears to be indicated 

 (1) by the similar nature, lithologically, of the materials composing 

 the bone horizon, (2) a similarity in the over and underlying strata, 

 (3) the likeness of the faunas from the two localities. If later 

 investigations show this provisional correlation to be correct, it is 

 of the utmost importance as definitely locating the horizon from 

 which the holotypes of the following species have come: Campto- 

 saurus dispar^ (J . 7nedius, G . naiius, C. hrowni, Di'yosaurus alius, and 

 Diracodon latlceps. Among the other dinosaurian genera recognized 

 from qfuarry No. 13 are Stegosaurus, Allosaurus, Coehmis, and 

 Moi-osaurus, as well as the turtle, Glyptops and the crocodile Goni- 

 opholis, and fish remains, which, however, are too fragmentary to 

 admit of identification. By comparing the faunal lists of the two 

 quarries, it will be observed that they are quite alike, although Bone 

 Cabin Quarry predominates in representatives of the Opisthocoelia 

 (Sauropoda), Quarry 13 in members of theOrthopoda (Predentata). 

 This observation would also apply to the relative numbers of indi- 

 viduals of each group found in the two quarries. Quarrj'^ No. 13, as 

 shown by the maps, was especially rich in stegosaurian and campto- 

 saurian remains. 



With the permission of Dr. F. B. Loomis, I reproduce (Plate 20, 

 figs. 1 and 2) sections of the Little Medicine and Como Bluff 

 exposures, which, according to his measurements, show the 5-foot 

 sandy layer No. 28 to be within 60 feet of the overlying Cretaceous 

 (Dakota). This is the highest known horizon of the Jurassic in 

 which camptosaurian bones have been found, and the discovery at 

 this level in the famous " Bone Cabin Quarry " of a skeleton of 

 C. namis (see Plate 19), strengthens somewhat the assumption of 

 the contemporaneity of this layer with the bone horizon of Quarry 13. 



« Bull. Amer. Mus. Nat. Hist, XIV, 1901, pp. 189-197, pi. xxvii, figs. 2, 3. 



