CRETACEOUS REPTILES OF THE UNITED STATES. 67 
the Mississippi river and the Rocky mountains, reaching north into British 
America, and south into Mexico. In New Jersey they are estimated to have 
a thickness of from four to five hundred feet; in the region of the Upper 
Missouri, from two to two thousand five hundred feet. 
Multitudes of fossils are found in the American cretaceous formations, though 
the species appear not to be so numerous as in those of Kurope. The mollusks 
are particularly abundant, and among them are a great many species of cham- 
bered shells. A species of ammonite is found on the Upper Missouri as large 
as an ordinary fore-wheel of a wagon. Remains of fishes are Tikewise numerous, 
but generally they are found in a very fragmentary condition. Scales, vertebree, 
and teeth, are usually the fossils which represent them. ‘The teeth of sharks 
are especially numerous. Bones of reptiles are also abundant, and their remains 
form the subject of the author’s memoir. As in the European cretaceous 
formations, no evidences have yet been discovered of the existence of birds or 
mammals in those of the United States. 
Most of ‘the reptilian remains described by the author have been derived 
from New Jersey, where they are constantly being discovered in the digging 
of marl for agricultural purposes. Various genera and species of the crocodile 
family existed during the cretaceous period, as indicated by their remains. 
Some of these had the skeleton constructed after the same pattern as those now 
living, while others were peculiar, or have no near representatives in existence. 
All living crocodiles, under which term we include the gavials and alligators, 
have the vertebre or bones of the spinal column, with their bodies concave in 
front and convex behind, so that they are firmly jointed in a ball and socket- 
like manner. Several species of extinct crocodiles, having the spinal column 
constructed in the same manner, have been discovered in the cretaccous lime- 
stone and green-sand of New Jersey and Delaware. One of the latter species, 
named Thoracosaurus neocesariensis, signifying the armor-covered saurian of 
New Jersey, resembled in its form and size the modern long-snouted gavial, or 
crocodile of the Ganges. A nearly entire skull of this animal was discovered 
imbedded in limestone on the farm of General William Irick, near Vincenttown, 
Burlington county, New Jersey, and is now preserved in the museum of the 
Academy of Natural Sciences of Philadelphia. Fragments of jaws and long, 
curved, conical teeth of the same species have been found in other localities of 
the State, as the highlands of Neversink, the vicinity of Blackwoodtown, Cam- 
den county, Big Timber creek, Gloucester county, and in Burlington county. 
Vertebre and other bones, including specimens of the strong osseous plates of 
the skin, have likewise been discovered in Burlington county. 
The skull of this crocodile, when perfect, has measured over a yard in length, 
and the whole animal about twenty-five feet. 
A species of the same genus, the Thoracosaurus macrorhynchus has been 
discovered in a cretaceous formation of France, and a fine skull of it is pre- 
served in the museum of the Jardin des Plantes, at Paris. 
Another extinct crocodile, named Bottosaurus Harlani, after Dr. Harlan, who 
