HALLOPUS, BAPTANODON, ATLANTOSAURUS BEDS 347 



any basis of comparison. Of the fishes a few species of Ceratodas 

 only are known, and inasmuch as this genus is supposed to range 

 from the Trias to the present time, these species have no correlat- 

 ing value whatever. 



To sum up: there is no valid vertebrate evidence pointing to an 

 age greater than the Purbeck for the Atlantosaurus beds, and but 

 very little for a greater age than that of the Wealden. 



Unfortunately, in most of the discussions hitherto the Atlanto- 

 saurus beds have been considered as of some brief epoch. The 

 faunas of the upper and lower parts have never been differentiated, 

 save in some exceptional cases. Marsh, indeed, rarely ever gave 

 any precise location for his type specimens, referring them simply 

 to Wyoming, Colorado, etc. The term "Upper Jurassic" has been 

 applied indiscriminately to the whole fauna, as it has, indeed, in the 

 textbooks to the fauna of the Hallopus beds. Hatcher was the first 

 to distinctly point out that the uppermost part of the beds might 

 include a part of the Lower Cretaceous; and Darton has recently 

 separated some of the upper part as Lower Cretaceous under the 

 name of "Lakota beds." 



I am strongly of the opinion that these deposits, nowhere, so far 

 as known, exceeding a thickness of 500 feet, really represent 

 various epochs between the Jurassic and the Upper Cretaceous, and 

 that sooner or later we shall have evidence to distinguish the later 

 from the earlier faunas. 



A year or two ago Mr. N. H. Brown, of Lander, Wyo., sent some 

 fish teeth to Mr. F. A. Lucas, of the National Museum, for deter- 

 mination. Mr. Lucas, after comparison with the type specimens 

 described by me from the Lower Cretaceous of Kansas, identified 

 them as species of Scyliorrhinus. In company with Mr. Brown, I 

 later examined the outcrop whence he had obtained his specimens, near 

 Lander, Wyo., and found it to be in the upper part of the Atlanto- 

 saurus beds, and some 15 or 20 feet below an outcrop containing 

 leaves which Mr. Knowlton identified as Dakota. A search in this 

 horizon disclosed numerous specimens of shark and crocodile teeth, 

 four species of which I identified with species obtained from the 

 mentor beds of the Lower Cretaceous, of Kansas, together with 

 numerous fragments of dinosaur bones, among which I recognized 



