M. Fore-and-aft diameter of crown ·010 Transverse diameter of crown ·007 Vertical height of crown Crocodilus clavis, Cope. U. S. Geol. Survey of Terrs. 1872, p. 612. This species is indicated by the remains of a crocodilian larger than _Crocodilus Elliotii_, but very different from it. The pitting of the dermal scutes, and of all the cranial bones, is deeper than in any other of the Bridger crocodilians in our possession, and very strongly resembles that in _Alligator mississippiensis_. The _mandible_ has a long symphysis, and the alveolar border shows the sudden deep depression just behind it, which is so marked in the ordinary alligator. The rami, however, do not diverge at such an open angle. The jaw is very stout, and is deeper and thinner than in _Crocodilus Elliotii_; and is of about the same proportionate thickness, but deeper than in the alligator. The splenial ends obtusely, and approaches the symphysis somewhat more closely than in the alligator, but does not enter into its formation. The teeth are stout and obtusely conical, not striate, and implanted very close together; they exhibit about the same alternation of size as do those of the alligator. What appears to be the canine is small; it is preceded by a much smaller, and succeeded by a slightly smaller tooth. The dermal scutes are quadrate in shape; they are deeply and irregularly pitted, and have a low but distinct longitudinal keel; they are suturally united by their lateral borders. CHELONIA. The Bridger beds have yielded a great abundance and variety of land, marsh, and fresh-water chelonians. They present much variation of form and size; and, owing to the great pressure in the strata, scarcely any two specimens of the same species are alike; occasionally, however, an undistorted specimen is obtained. The most abundant remains of turtles are those of a species of the recent genus _Emys_, which are found in all the beds, and are, perhaps, the commonest fossils of the basin. The genera _Trionyx_ and _Hadrianus_ (_Testudo_, Leidy) follow next in order. HADRIANUS, Cope. Resembles _Testudo_ in form, but has two analscuta, as have most _Emydidæ_. Hadrianus allabiatus, Cope. U. S. Geol. Survey of Territories, 1872, p. 630. Represented by two ungual phalanges which resemble the claws of _Testudo_, but are proportionately shorter, broader, and not so pointed at the ends. They are oval in section, both longitudinally and transversely; the articular faces are deep and subinferior. From Henry's Fork. Hadrianus octonarius, Cope. Geol. Survey of Terrs., 1872. p 630. Represented by the right humerus of a large individual.