1. Palaeoscincus costatus, Leidy.

The genus and species are founded on a single specimen of a tooth of a lacertian, discovered by Dr. Hayden.

The crown of the tooth is palmate, with eight radiating costae terminating at the margin in more or less developed points. The fang is flattened cylindrical, and is hollow; and it expands into a ridge surrounding the base of the crown. Breadth of the crown 4 lines, length 2 1/2 lines; width of the fang 2 lines, thickness 1 line. Whole length of the specimen 4 lines.