1. anterior nares. 2. prominence on the nasal bones which probably carried a horn. 3. pre-orbital vacuity. 4. orbit. 5. scapula. 6. coracoid. 7. ilium. 8. pubis (pre-pubis). 9. ischium.] The nares have the form of long slits and there are large pre-orbital vacuities. The limb bones are solid, and the anterior limbs are not much shorter than the posterior ones. All the limbs are plantigrade and pentedactylate, and the digits of the pes are clawed. There is a large pre-pubis directed downwards and forwards, meeting its fellow in a ventral symphysis, but there is no post-pubis. The Sauropoda are found in the secondary rocks of Europe and N. America and include the largest land animals that are known to have existed. Many of the best known forms such as _Brontosaurus_ and _Morosaurus_ are North American. _Suborder (2)._ THEROPODA. The members of this suborder were all carnivorous, and from the small comparative size of the anterior limbs many of them were probably bipedal. The vertebrae are opisthocoelous or amphicoelous, their neural arches are provided with zygosphenes and zygantra, and their centra are frequently hollowed internally; the limb bones are also hollow, and in fact the whole skeleton is extremely light. The tail is of great length. The teeth are pointed and recurved, and have one or both borders serrated; they are always planted in distinct sockets, and some of them are borne by the premaxillae. There are large pre-orbital vacuities. The digits of both manus and pes are terminated by pointed ungual phalanges which must have borne claws. In the pelvis the pre-pubes and ischia are slender bones, the former meeting in a ventral symphysis. The ilia are very deep vertically and there are no post-pubes. The astragalus is closely applied to the tibia, in front of which it sends an ascending process, sometimes the two bones appear to have been ankylosed together, as in birds. The metatarsals are elongated and the feet digitigrade. The Theropoda vary greatly in size, one of the best known genera _Compsognathus_ was about as large as a cat, another, _Megalosaurus_, perhaps as large as an elephant. _Ceratosaurus_ is the name of a well-known North American form regarded by many authorities as identical with _Megalosaurus_. _Suborder (3)._ ORTHOPODA. This suborder includes the most specialised of the Dinosaurs, certain of which resemble the Theropoda in being bipedal. In some of them such as _Stegosaurus_ the exoskeleton is strongly developed, in others such as _Iguanodon_ it is absent. The vertebrae are solid and may be opisthocoelous, biconcave, or flat. The teeth are compressed and serrated, often irregularly, and are frequently not set in distinct sockets. The anterior part of the premaxillae is without teeth, and a toothless predentary or mento-meckelian bone is present. The pre-orbital vacuities are small or absent, and the nares are large and placed far forwards.