In the American Journal of Science in 1877, the writer described a remarkable extinct reptile from Colorado, under the name Stegosaurus armatus, and later a much more perfect specimen of another species, Stegosaurus ungulatus, from essentially the same horizon, in the Jurassic of Wyoming. The latter specimen was in fine preservation, and the more important parts of the skull and skeleton, and especially of the remarkable dermal armour, were secured. Subsequently, more than twenty other specimens of these and other species were obtained, so that nearly every part of the osseous structure thus became known, and only portions of the dermal armour were in doubt. A fortunate discovery cleared away most of the doubt in regard to one species, Stegosaurus stenops, as the type specimen had the skull, skeleton, and dermal armour together when entombed, and almost in the position they were when the animal died.