HALLOPUS, BAPTANODON, ATLANTOSAURUS BEDS 341 



characters of Hallopus are shown especially in the sacrum. The 

 type specimen, as Marsh has said, came from an horizon far below 

 the lowermost of those yielding sauropodous remains. Hatcher has 

 said that "no fossils have been obtained from the Red Beds of Garden 

 Park" — an error. 



BAPTANODON BEDS 



From the Baptanodon beds of Wyoming three genera and eight 

 species of vertebrates have been described: Baptanodon discus Marsh, 

 B. natans Marsh, B. marshi Knight, Pantosaurus striatus Marsh, 

 Megalneusaurus rex Knight, Cimoliasaurus laramiensis Knight, 

 Plesiosaurus shirleyensis Knight, and Diplosaurus nanus Marsh. 

 Of these I am not satisfied of the distinction between Pantosaurus 

 striatus and Plesiosaurus shirleyensis. 



On the evidence which seemed to be presented by Baptanodon, 

 Hatcher was inclined to refer these beds to the Middle Jurassic: 

 "The vertebrates of these marine beds point to a somewhat greater 

 antiquity than do the invertebrates, for Baptanodon, the most abundant 

 and best-known form, has its nearest ally in the Ophthat 'mo saurus oi 

 Europe;" 1 from which, as he rightfully says, it is scarcely distinguish- 

 able generically. While O phthalmosaurus is typically 2 from the Middle 

 Jurassic, another species 3 has been described from the Cambridge 

 Greensand (Upper Cretaceous). While it is very possible, indeed 

 not improbable, that these two species are not congeneric, it is also 

 apparently quite true that Baptanodon seems to be as closely allied 

 to the Cretaceous as to the Jurassic species. Indeed, in speaking of 

 the Cretaceous form, Lydekker says: "This species may belong in 

 Baptanodon." It is therefore evident that, so far as our knowledge 

 yet goes, Baptanodon is worthless as a Leitfossil. 



In a later, posthumous 4 , paper Hatcher has said : " that these beds 

 are of Upper Jurassic has not been questioned, and is abundantly 

 •confirmed by both their vertebrate and invertebrate faunas;" from 

 which it is evident that he later placed no value on the relationships 



1 Memoirs of the Carnegie Museum, Vol. II (1903), p. 71. 



2 O. icenicus Seeley, Quarterly Journal of the Geographical Society, Vol. XXX 

 1(1874), p. 696. 



3 O. cantabrigiensis Lydekker, ibid.; Geological Magazine (3), Vol. V (1888), 

 p. 310. 



4 Proceedings of the American Philosophical Society, Vol. XLIII (1904), p. 354. 



