The largest species of this genus at present known may be called Morosaurus robustus. It can readily be distinguished from those already described by its short, helmet-shaped, ilium, which is represented in Plate VIII, figures 1 and 2.

One species of this genus, Morosaurus grandis,* is now known by a nearly complete skeleton, and the remains here figured are mainly portions of this individual. They were found together in nearly as perfect preservation as in life, and many of them were in their natural position. The locality was in Wyoming, and the bones were taken out with great care by Mr. S. W. Williston of the Yale Museum.

This animal when alive was about forty feet in length. It walked on all four feet, and in many other respects was very unlike the typical Dinosaur. It must have been very sluggish in all its movements. Its brain was proportionately smaller than in any known vertebrate.

Diplodocus longus, gen. et sp. nov.

This genus includes some Dinosaurs of very large size, and herbivorous in habit. It may be distinguished from the genera already known by the caudal vertebrae, which are elongated, deeply excavated below, and have double chevrons, with both anterior and posterior rami. (Plate VIII, figures 3 and 4). To the last character, the generic name refers. The tibia, also, is a very characteristic bone, as it is deeply grooved above to receive the fibula. The feet in this genus are very similar to those of Morosaurus, shown in Plate VII.

The present species is based upon one posterior limb, and the tail, of a single individual. The limb, as extended before removal, measured from the head of the femur to the end of the toes over thirteen feet (4·1). The femur was 1645mm in length, and the tibia 1090mm. Four of the median caudal vertebræ measured together thirty-four inches (760mm). The first of these, or the fourteenth in the series, was eight and one-half inches (217mm) long, and five and one-half inches (140mm) across the anterior end.

The peculiar chevron represented in Plate VIII, figure 3, was found attached to the eleventh caudal, and all the remaining chevrons observed were of this character. Figure 4 represents a specimen found at another locality, and perhaps belonging to a different genus.

The above remains indicate a reptile about fifty feet in length. They were found in the upper Jurassic, near Cañon City, Colorado, in 1877, by Mr. S. W. Williston.

* This species, when described by the writer, was referred provisionally to the genus Apatosaurus. This Journal, vol. xiv, p. 515.

Laosaurus Marsh, 1878.

Another well marked group of herbivorous Dinosaurs, mostly of small size, occur in the same deposits with the gigantic forms. above described. These belong to a separate suborder, and among the typical Ornithoscelida, as defined by Huxley. They belong also to the Iguanodontidae, and most nearly resemble the genus Hypsilophodon, from the Wealden of England. All the specimens known from the Atlantosaurus beds appear to come under the genus Laosaurus, several species of which have already been found, represented by numerous individuals. One of the species hitherto undescribed may be called Laosaurus altus, and its remains, with those of the smaller Laosaurus celer, are here used to define the characters of the genus.

*

The skull is of medium size, and, so far as its structure has been made out, resembles that of Hypsilophodon. The teeth, also, are very similar (Plate IX. figures 2 and 3.) The rami of the lower jaw are edentulous in front, and apparently were not united by symphysis. The dorsal and caudal vertebræ have their extremities nearly plane, and the neural arches are united to the centra by suture. The chevrons have their articular ends joined together, as in Iguanodon and most Dinosaurs.

The fore limbs were quite small, less than half as long as the hind limbs, and evidently were not much used in locomotion. The humerus is slender, and considerably curved. The radius and ulna are nearly of the same size. In this species, the humerus is 190mm long, and the radius 150.

The bones of the pelvis are distinct. The outline of the ilium is not known, but the pubes and ischia of several individuals have been determined, and prove of great interest. The pubis forms the antero-inferior part of the acetabulum, and the ischium completes the lower portion. The pubis extends downward and inward in front, and terminates in a broad spatulate free extremity. It unites with the ischium below the acetabulum, and sends backward and downward a long slender ramus, which is clearly homologous with the so-called pubic bone in birds (Plate X, figure 2). There is a large foramen near the ischiadic margin. This foramen is closed behind by suture only, and in some specimens becomes a notch. The posterior, rodlike, ramus ossifies from an independent center, and, to distinguish it from the true reptilian pubis in front, may be called the post-pubic bone. comparison of the three pelves represented together in Plate X (Hesperornis, Laosaurus and Morosaurus), will make clear the intimate relation existing between the pubic bones of Birds and Dinosaurian reptiles. If this series be extended by adding

*This Journal, xv, 244, March, 1878.

A

After these figures were made, showing the position of the Dinosaurian pubis, which has caused so much discussion since Cuvier, I found that Dr. J. W. Hulke had already suggested the true solution of one difficulty. (Journal Geological Society of London, vol. xxxii, p. 334.)

AM. JOUR. SCI.-THIRD SERIES, VOL. XVI, No. 95.-Nov., 1878.

26a

the pelves of some existing birds (for example Geococcyx), and of a few other reptiles, it will become still more evident that the bone called "pubis" in a bird, is a different bone from the pubis of a crocodile. The ischium in Laosaurus is a slender bone, extending backward parallel with the post-pubic. It has a distinct obturator process, which laps over the latter bone.

The limb bones in this genus have a distinct medullary cavity. The femur has a prominent great trochanter, the extremity of which is separated from the neck by a fissure. The third trochanter is long, and curved outward. The tibia slightly exceeds the femur in length, the proportions in Laosaurus altus being 393 to 360mm (Plate IX, figure 3). The fibula is slender, and the distal smaller than the proximal end. The astragalus is distinct from the tibia, and the calcaneum supports the fibula. There are but two tarsals in the second row. There are three well developed digits in the pes (II, III and IV). The outer, or fifth, is wanting, and the first, or hallux, is represented only by a remnant of the metatarsal. The phalanges are rather short, and the ungual ones are pointed. (Plate IX, figure 3.)

The remains of this genus at present known are all from the Atlantosaurus beds of Colorado and Wyoming. Those here described were found in Wyoming by Mr. S. W. Williston. They represent an animal of slender proportions, and about ten feet in length.

Yale College, New Haven, October, 1878.

[To be continued.]