516
O. C. Marsh—New Dinosaurian Reptiles.
the middle part being so diminished as to greatly reduce the strength. The vertebræ preserved are biconcave, with shallow cavities. The feet bones referred to this species are very slender. A lumbar vertebra has its centrum 105 mm. in length, and 89 in least transverse diameter. An anterior caudal, 35 mm. long, has its centrum so much constricted that its least transverse diameter is 38 mm., while its anterior face is 90 mm. in transverse diameter.
The animal indicated by the remains preserved was from fifteen to twenty feet in length. All the known specimens are from the upper Jurassic of Colorado.
A diminutive Dinosaur, about as large as a fox, is indicated by some remains in good preservation, the most characteristic of which is a nearly perfect femur. In this bone, the great trochanter is prominent, and the third trochanter especially so. There is a well developed fibular ridge, directed outward and backward. The cavity in this bone is unusually large, and the walls are smooth. This femur agrees so nearly with that of the type of Nanosaurus, that the present species may be provisionally referred to that genus.
The dimensions of this bone are as follows:
Length of femur....................................................................................................................................................................................................................................................100·mm
Distance from head to middle of third trochanter....................................................................................................................................................................................................................................................30·
Transverse diameter of distal end....................................................................................................................................................................................................................................................21·
Greatest antero-posterior diameter....................................................................................................................................................................................................................................................18·
Least transverse diameter of shaft....................................................................................................................................................................................................................................................11·
Diameter across third trochanter....................................................................................................................................................................................................................................................15·
The known remains of this reptile are from the upper Jurassic of Colorado.
The specimens described in the present articles are deposited in the Peabody Museum of Yale College. They are all from essentially the same geological horizon, which I find to be upper Jurassic. The deposits which contained them may be called the Atlantosaurus beds, from their most characteristic fossils, the huge Dinosaurs of that genus.
Yale College, New Haven, November, 1877.
