750 



SCIENCE. 



[N. S. Vol. XVI. No. 410. 



terygians, with the Chimseroid fishes, and even 

 with the tetrapod Stegocephalia. He con- 

 eludes that the Placoderms in this larger sense 

 are true fishes, and that among them the Coc- 

 costeids occupy an ancestral position, on the 

 one hand to the ancient Ganoids and to the 

 Chimseroids; on the other hand, they show 

 relationships to the Stegocephalia and Am- 

 phibia. 



These views difl^er very widely from those 

 recently presented afresh by Patten in the 

 American Naturalist, who regards the Ostra- 

 coderms, especially as seen in the Tremataspis 

 form, as intermediate between Crustacea some- 

 what of Limulus type and vertebrates. 



ORIGIN OF THE TURTLES. 



Still more important is Dr. Jaekel's de- 

 scription of a new Placodont* from the Upper 

 Triassic, which he names Placochelys placo- 

 donta, owing to the fact that he believes it 

 constitutes a toothed ancestor or collateral of 

 the turtles. Since Placodus and the related 

 form of Cyamodus have hitherto been placed 

 by Zittel and others near the Anomodont rep- 

 tiles, the discovery of an animal which unites 

 the skull of the Placodus type with the armor- 

 ed skeleton of the Chelonian type is most 

 interesting. Dollo had already predicted the 

 existence of toothed turtles, and the present 

 reviewer was strongly of the opinion that Placo- 

 dus belonged much nearer the turtles than the 

 Anomodonts. This new animal, Placochelys, 

 suggests to the author the ancient Ehyncho- 

 cephalian Hyperoadapedon. The structure of 

 the skull and other parts of the skeleton is not 

 at all like that of the Anomodonts ; on the other 

 hand, it is more similar to that of primitive 

 Plesiosaurs such as Nothosaurus and Pisto- 

 saurus. This would confirm Baur's opinion 

 of the strong original relations between Ple- 

 siosaurs and Chelonia. The carpus, as well as 

 the skull structure and spread of the ribs, 

 points to resemblances especially to Chelonia 

 of the order Pleurodira. 



* ' Ueber Placochelys n. g. nnd ihre Bedeutung 

 fiir die Stammesgeschichte der Schildkroteii,' 

 Sep.-Abd. a. d. ^Neuen Jalirh. f. Min., Geol. u. 

 Pal., 1902, Bd. I. 



ABANDONMENT OF THE OLIGOCENE AND MIOCENE 

 LAKE BASIN THEORY. 



Hatcher's recent discussion* of the origin 

 of the Oligocene and Miocene deposits of the 

 great plains, following the argument strongly 

 presented by Dr. W. D. Matthew in his memoir 

 ' Fossil Mammals of Northeastern Colorado,' 

 appears to give the death blow to the lake 

 basin theory of most of the great deposits east 

 of the Eocky Mountains. The earlier writers, 

 including David Dale Owen, King, Hayden, 

 Leidy, Cope, Marsh and others, were always 

 accustomed to speak of these deposits as lacus- 

 trine, and they are at present, or were until 

 very recently, so considered by many authori- 

 ties, such as Todd, Scott, Dalton. While the 

 Lower Oligocene or White River series are 

 largely composed of river and flood-plain de- 

 posits, Mr. Hatcher shows the absence of any 

 evidence of the existence of a great lake. He 

 adds to the observations of Matthew numerous 

 geological and faunal observations of his own, 

 such as the occurrence of shallow water forms 

 of plants and animals, characteristic of small 

 springs, shallow ponds and brooks, remains of 

 forests, and the absence of remains of croco- 

 diles, turtles and fresh-water fishes. He con- 

 cludes : " The above facts, together with those 

 brought forward by Dr. Matthew, have driven 

 me, contrary to my earlier opinion, to reject 

 the theory of a great lake and accept that of 

 small lakes, flood-plains, river channels and 

 higher grass-covered pampas as the conditions 

 prevailing over this region in Oligocene and 

 Miocene times." 



STUDIES OF EOCENE MAMMALIA IN THE MARSH 

 COLLECTION, PEABODY MUSEUM. 



The first part of these very interesting and 

 important studies by Dr. J. L. Wortmanf have 

 now been published in collected form, making 

 a bulletin of 144 pages, abundantly illustrated 

 with pen drawings, including the description 



* ' Origin of the Oligocene and Miocene De- 

 posits of the Great Plains.' Proc. Am. Phil. Soc, 

 xli., Apr., 1902, p. 113. 



t ' Studies of Eocene Mammalia in the Marsh 

 Collection, Peabody Museum, Part I., Carnivora,' 

 Amer. Jour, of Science, Vols. XI.-XIV., 1901- 

 1902. 



