The _pelvis_ is represented by the acetabulum and a small portion of ilium and ischium. They resemble the corresponding parts in the skeleton of _Stenops gracilis_. The acetabulum is a long oval, not subcircular, deep, and quite narrow from side to side. It appears to be directed nearly straight outwards. The ilium is narrow, has a concave gluteal surface, and a prominent acetabular border. The pubis evidently projected forward, making a right angle with the ilium; while the ischium is slender and nearly in the same plane with the ilium. The femur is thoroughly lemurine in shape. The shaft, (as much of it as is preserved), is straight and sub-cylindrical; it is not flattened even distally, but becomes very thick and trihedral in shape just above the trochlea. The trochlea is long, and rises obliquely upon the shaft; the groove is deep, and the two divisions are asymmetrical, the external somewhat the larger. The condyles are large. They are but slightly convex in either direction and project backwards, and are broadest posteriorly. The internal is the larger. They are separated by a deep but not wide popliteal groove, which does not extend into a popliteal fossa. The position and shape of the condyles are such as show that the femur must have been very oblique to the tibia, as in the other lemurs. The tuberosities, especially the internal, are very large and prominent. The whole distal end has an asymmetrical appearance, owing to the greater size of the internal condyle. _Measurements._ M. Breadth of ilium at acetabulum ·0065 Vertical diameter of acetabulum ·007 Transverse diameter of acetabulum ·009 Fore-and-aft diameter of shaft of femur above trochlea ·0065 Transverse diameter of shaft above trochlea ·0065 Width of trochlea ·004 Length of trochlea ·0075 Breadth over condyles ·010 Breadth of inner condyles ·005 OLIGOTOMUS, Cope. Ann. Rep. U. S. Geol. Survey of the Terrs., 1872, p. 607. "Molars constructed much as in _Hyopsodus_ and _Lophiotherium_, viz., with two external subtrihedral cusps which wear into crescents, the posterior connected by a low oblique ridge with the basis of the anterior cone of the inner side; the latter with two conic cusps. It differs from these genera and from _Orotherium_ in the possession of two premolars; the inferior molars are probably six, leaving four true molars." Oligotomus cinctus, Cope. Loc. cit. Represented in our collection by the penultimate lower molar, and a caudal vertebra, which has a remarkably long, slender, and simple centrum, with rudimentary metapophyses. OPISTHOTOMUS, Cope. Wheeler's Survey, Pal. v. iv., pt. 11, p. 152.