The expedition collected parts of four species of birds; a feather from Florissant Col. the distal ends of a humerus, and a femur and a portion of the shaft of an ulna (?) from the Bridger beds, but they are all too uncharacteristic for classification or description. REPTILIA. CROCODILIA. CROCODILUS. Crocodilus aptus, Leidy. Contributions to Extinct vertebrate fauna of the Western Territories, p. 126. Henry's Fork. Crocodilus Grinnelli, Marsh. American Journal of Science and Arts, vol. i., p. 465. From Cottonwood Creek. Crocodilus Elliotii, Leidy. Cont. to Ex. Vert. Fauna, p. 126. Represented by a perfect skull, and several vertebræ. This fossil exhibits a form of skull which shows characters of both crocodile and alligator; the latter to a less marked degree. That it properly belongs to the former genus is shown by the notch in the upper jaw which receives the canine of the lower. The entire skull is remarkably flat on its upper surface, the face and cranium being nearly in the same plane without the descent at the frontals usual in these reptiles. The jaw is deeply notched at the sutures between the maxillaries and pre-maxillaries, and the second maxillary notch is well marked. All the bones of the upper surface of the head are deeply pitted. The borders of the cranium are rounded as they approach the orbits; the superior temporal orifices are almost perfectly circular, the fore-and-aft diameter exceeding the transverse by only one millimetre. This effect may, in some degree, be due to distortion. To give a more detailed account of the several elements of the skull, we take up first the _basioccipital_. This bone is remarkably long and straight, tapers gradually downwards, and becomes quite narrow at the distal end. It is smooth throughout, and exhibits no rugose muscular attachments, such as are sometimes seen in other members of the order. The condyle is large and nearly spherical, but with median groove distinctly marked. In size and shape it is more like that of the alligator than of the ordinary crocodile, but it is somewhat different from either. It differs from the former, in not having so long a neck distinctly marked by a constriction; and from the latter, in not having additional articular faces on each side of the condyle proper. As far as can be judged, no portion of it is formed by the exoccipitals. Below the condyle the basioccipital is perforated by two small vascular foramina; the spheno occipital canal occupies the usual place, and is very large.