810 STRATIGRAPHICAL GEOLOGY. — [Boox VI. 
chodon), and some others. From the same limited horizon also 
the bones of at least two species of birds have been obtained. 
In recent years the most astonishing additions to our knowledge 
of ancient reptilian lite have been made from the Cretaceous rocks of 
western North America, chiefly by Professors Leidy, Marsh, and 
Cope.’ According to a recent enumeration made by Mr. Cope, but 
which is already below the truth, there were known 18 species 
of deinosaurs, 4 pterosaurs, 14 crocodilians, 13 sauropterygians or 
sea-saurians, 48 testudinates (turtles, &c.), and 50 pythonomorphs 
or sea-serpents. One of the most extraordinary of reptilian types 
was the Discosawrus or Elasmosaurus—a huge snake-like form 40 feet 
long, with slim arrow-shaped head on a swan-like neck rising 
20 feet out of the water. This formidable sea-monster “ probably 

Fic. 396.—Cretactous CErrHALOPops. 
a, Belemnitella plena (Blainv.) (4); b, Belemnitella mucronata (Schloth.) (4); 
c, Nautilus danicus (Schloth.) (3). 
often swam many feet below the surface, raising the head to the 
distant air for a breath, then withdrawing it and exploring the 
depths 40 feet below without altering the position of its body. 
It must have wandered far from Jand, and that many kinds of 
fishes formed its food is shown by the teeth and scales found 
in the position of its stomach” (Cope). ‘The real rulers of the 
American Cretaceous waters were the pythonomorphie saurians or 
sea-serpents, in which group Mr. Cope includes forms like Mosa- 
saurus, of which upwards of 40 species have been discovered. 
Some of them attained a length of 75 feet or more. They possessed 
1 Leidy, Smithson. Contrib. 1865, No. 192; Rep. U. 8S. Geol. and Geograph. Survey of 
Territories, vol, i. (1873); Cope, Rep. U.S. Geol. and Geograph. Survey of Territories, 
vol. ii. (1875); Amer. Naturalist, 1878; Marsh, Amer, Journ. Science, numerous papers 
in 3rd series, vols. i.—xxil. 
