The Cambridge specimens manifestly belong to at least three genera. Something may be said of the characters of the large animals which are included in the genus Ornithocheirus. These fossils have many points of structure in common with the great American toothless forms which are of similar geological age. The skull is remarkable for having the back of the head prolonged in a compressed median crest, which rose above the brain case, and extended upward and over the neck vertebræ, so as to indicate a muscular power not otherwise shown in the group. For about three inches behind the brain this wedge of bone rested on the vertebræ, and probably overlapped the first three neural arches in the neck. Another feature of some interest is the expansion of the bone which comes below the eye. In Birds this malar or cheek bone is a slender rod, but in these Pterodactyles it is a vertical plate, which is blended with the bone named the quadrate bone, which makes the articulation with the lower jaw in all oviparous animals. The beak varies greatly in length and in form, though it is never quite so pointed as in the American genus, for there is always a little truncation in front, when teeth are seen projecting forward from a position somewhat above the palate; the snout is often massive and sometimes club-shaped. Except for these variations of shape in the compressed snout, which is characterised by a ridge in the middle of the palate, and a corresponding groove in the lower jaw, and the teeth, there is little to distinguish what is known of the skull in its largest English Greensand fossils from the skull remains which abound in the Chalk of Kansas. This English genus Ornithocheirus, represented by a great number of species, had the neural arch of the neck bones expanded transversely over the body of the vertebra in a way that characterises many birds with powerful necks, and is seen in a few Pterodactyles from Solenhofen. It is difficult to resist the conclusion that the neck vertebræ were not usually more than twice to three times as long as those of the back, and it would appear that the caudal vertebræ in the English Cretaceous types were comparatively large, and about twice as long as the dorsal vertebræ. Unless there has been a singular succession of accidents in the association of these vertebræ with the other remains, Ornithocheirus had a tail of moderate length, formed of a few vertebræ as long as those of the neck, though more slender, quite unlike the tail in either the long-tailed or short-tailed groups of Solenhofen Pterodactyles, and longer than in the toothless Pterodactyles of America. [Illustration: FIG. 70. CERVICAL VERTEBRA, ORNITHOCHEIRUS Under side, half natural size. (Cambridge Greensand)]