86 0. C. Marsh—American Jurassic Dinosaurs. 
This reptile may be called Sauranodon natans, and the order 
it represents Sauranodonta is genus bears a similar relation 
to the Ichthyosaurs that Pteranodon does to the true Pterodae- 
tyls, and it is interesting to find the two highly specialized 
forms preserved in the same region. 
The geological horizon of the Sauranodontide, so far as now 
known, is in the Ju rassic, immediately below the Atlantosaurus 
beds. The accompanying fossils are Ammonites and Belem- — 
nites, showing more distinctly marine deposits, which may be 
called the Sauranodon beds. 
Yale College, New Haven, December 27, 1878. 
Art. X.—Principal Characters of American Jurassic Dinosaurs; 
by Professor O. C. MarsH. Part II. With eight Plates. — 
In a previous article Moe xvi, p. 411, Nov., 1878), the 
writer gave a short account of the geological ‘horizon’ and : 
accompan ying! scone of the a urassic Dinosaurs recently foundin — 
untains ; and also state : 
is illustrated by new reguiipled and tne the neler parts 
in some recent birds. 
Apatosaurus Marsh, 1877.* 
The genus Apatosaurus may be readily distinguished from 
Morosaurus by the sacrum, which consists of only three verte 
bree instead ot four (Plates V and VI, figures 1 and 2. 
ischium, also, has its distal end ‘expande d. The scapula, like 
wise, is quite ‘different, its superior extremity, being without the. 
anterior extension seen in Morosaurus (Plate + So far as at 
* This Journal, vol. xiv, p. 514. 
