348 5. W. WILLISTON 



the genus Laosaurus described by Marsh from the Atlantosaurus 

 beds. 



It may be objected that the specific identity of fish teeth is too 

 doubtful to correlate such remote horizons, and the objection might 

 be valid for single specimens, or even possibly for single species. 

 In this case, however, I did not find a single form that was not repre- 

 sented in the Kansas beds, and the specimens were abundant. 

 Furthermore, the matrix containing the fossils is so nearly identical 

 with that from Kansas that, had anyone given me specimens, without 

 information of their derivation, I should have unhesitatingly referred 

 them to the Kansas beds. The fact, moreover, is of interest as 

 showing a marine fauna. This horizon in Kansas contains not only 

 these species of fishes, but also crocodiles and dinosaurs which I am 

 unable to differentiate from forms from the Atlantosaurus beds, 

 and the Lander horizon contains fossils described by Marsh from the 

 Atlantosaurus beds. The Kansas horizon is high up in the Lower 

 Cretaceous. 



About 50 feet below this outcrop of Lower Cretaceous fossils 

 fragments of Sauropodous dinosaurs occurred in the Lander region. 

 The entire thickness of the Atlantosaurus beds here is not more 

 than 250 feet, to the best of my knowledge. 



The upper part of the Atlantosaurus beds is, it seems to me, 

 indisputably Cretaceous; the lowermost part is probably not older 

 than the Wealden, though possibly of Purbeckian age. I therefore 

 strongly protest against the common usage of referring all the fossils 

 from these beds to the Upper Jura. Until more is known of the 

 different faunas contained in it, the only proper designation for the 

 composite faunas included in them is Jura-Cretaceous; this assumes 

 that the Wealden is really Jurassic. 



I may add that I cannot agree with Mr. Hatcher in his use of the 

 name "Atlantosaurus beds" for these deposits. The name Atlanto- 

 saurus, it is generally conceded, has no place in zoological literature. 

 His comparison with Fort Union is hardly parallel. Nor can I adopt 

 the name "Sauropoda" for the Opisthocoelia of Owen. No one has 

 ever been in doubt as to what the term Opisthocoelia included, and 

 where every student knew its meaning, a precise definition is super- 

 fluous. 



