JURASSIC PERIOD. 433 



Upper Triassic. An Ammonite is represented in Figs. 759, 759 a; a 

 species of the genus Trigonia, in Fig. 757. 



Reptiles. — Remains of gigantic Reptiles occur in the Upper Ju- 

 rassic of Colorado (near Morrison and Canon City) and of Wyoming, 

 in beds called by Marsh, their first describer, Atlantosaurus beds. 

 They include Dinosaurs, both herbivorous and carnivorous, Crocodil- 

 ians, Pterodactyls or flying-reptiles (see p. 446), and Tortoises, along 

 with fishes of the genus Ceratodus. The Dinosaurs were either (1) 

 Saurian-footed, having four or five toes to the hind-foot ; or (2) Bird- 

 footed, having three toes to the same. Of the former a species of 

 Atlantosaurus (A. immanis Marsh) had a femur over eight feet long, 

 and a total length of nearly 100 feet ; the related Morosaurus grandis 

 Marsh (Plate I.), was forty feet long ; and Apatosaurus Ajax (Plate 

 II.), had the vertebrae of the neck (Fig. 1) four feet broad, and a sacrum 

 of three united vertebras (Fig. 3). Of the latter division, the slender 

 Laosaurus alius Marsh, about ten feet long, was strikingly bird-like, 

 Plate III. ; and species of Creosaurus Marsh were carnivorous. 



Mammals. — The marsupials, Dryolestes prises Mh., Stylacodon gra- 

 cilis Mh., and others occur with the above Reptiles. (See p. 852.) 



Characteristic Species. 



Actuals. — 1. Radiates. — Fig. 755, Pentacrinus asteriscus M. & H. 



2. Mollusks. — (a.) Lamellibranchs. — Fig. 756, Monotis curta, from the Black 

 Hills ; Fig. 757, Trigonia Conradi M. & H., ibid. ; 758, Tancredia Warveniana M. & 

 H., ibid, (b.) Cephalopods. — Fig. 759, young specimen of Ammonites cordiformis M. 

 & H., ibid.; Fig. 759 a, side-view of the same ; Fig. 760, Belemnites densus M. & H., 

 the upper part broken away, ibid. 



The Jurassic beds of Genesee valley, Plumas County, California, contain a Belemnite, 

 Trigonia pandicosta M., a Gryphcea near G. vesicularis Br., Jnoceramus (?) obliquus M., 

 /. (?) rectangulus M., Rhynehonella gnathophora~bL, and others of the genera Lima, 

 Pecten, Mytilus, Astarte, Unicardium, Myctcites, and Terebratula. In the beds of the 

 Uintah Mountains occur Pentacrinus asteriscus, Belemnites densus, two Trigonias, Gry- 

 phcea calceola, Myophoria lineata, Camptonectes bellistriatvs, Eumicrotis curta, etc. 



Among the Arctic fossils of this period, there are, at Prince Patrick's Land, Ammo- 

 nites yPClintocki, a species near A. concavus Sow., of the Lower Oolite; and at Cook's 

 Inlet, Ammonites Wosnessenski, A. biplex Sow. (?), Belemnites pa xillosus (B. niger 

 List ?), and Pleuromya unhides Br. ( Unio liassinus Schubler). A. biplex also is reported 

 to occur in the Chilian Andes, in latitude 34° S., as well as in Britain and Europe. 



2. Foreign. 

 I. Rocks: kinds and distribution. 



The strata of the Jurassic period in England (see map, page 344, on 

 which the areas numbered 7, 8 are Jurassic) appear at the surface 

 over a narrow range of country (averaging thirty miles in width), com- 

 mencing at Lyme-Regis and Portland on the British Channel, and 

 extending across England, north of northeast, to the river Humber, 

 and still farther north, on the eastern coast of Yorkshire, almost to 



