with double cup-shaped segments. Here was a dilemma! The ichthyornis had on what seemed reliable data been adjudged a bird; but not only was no bird ever known to have teeth set in sockets, but no bird had ever yet differed so far from its fellows as to affect teeth at all, not to mention the fact of its having resuscitated the fashion of a by-gone day in having its spinal vertebræ cupped at both ends. When it lived, was this creature, in which the types have become so strangely mixed, a reptile, or after all a bird? was a question that for a time made the brows of the philosophers anxious even in the midst of their happiness at the new discovery. They finally declared for the latter. There was, therefore, no resource left but to extend the boundaries which had hitherto confined the avian territory, and institute a new sub-class for its reception, whereat the ornithologists were greatly pleased and cordially welcomed the tooth bills among their feathered friends.
Among the treasures which on December 7, 1872, Prof. Marsh and his Yale College explorers brought back to New Haven, as the results of their autumn reaping among the Rocky Mountains, was the nearly entire skeleton, containing all the missing bones, of the royal hesperornis and of another bi-concave vertebrated bird.
The breastbone of the gigantic diver of the chalk is thin and weak, and entirely without a keel; in front it resembles the ostrich's or that of the apteryx of New Zealand—a group of birds presenting the greatest range in time and also the widest geographical distribution over the globe—but in some respects it approaches to the penguin's also. The wing-bones are diminutive, and the wings are rudimentary and useless as organs of flight. The bones that girdle the thigh clearly exhibit a resemblance to the corresponding bones of a cassowary; yet, although avian in type, they are peculiar and present some well-marked reptilian proclivities.
Furnished with these bones alone, and judging from his experience of bird architecture, in plan hitherto undeviated from, no ornithologist would have hesitated to relegate the remains to a place among the birds; and, had he been asked to restore the missing portions, he would in all probability have devised some cross between the corresponding parts of the divers, of the dabchicks (for their knee-cap resembles that of the hesperornis), and of the ostrich-like birds, adding thereto a tail somewhat after the model of the penguin's. Certain it is, however, he would never have approached the features presented by the actual bones. This primeval bird possessed a skull in its general form like that of the great northern diver, but with a less pointed beak. The jawbones, however, though they were originally covered with a horny bill as in ordinary birds, are widely different. They are massive and have throughout their length a deep groove which was thickly set with sharp-pointed teeth—evidence of carnivorous habits—their crowns covered with enamel and supported on stout fangs. In form of crown and base they most resemble the teeth of the reptiles found in the Maes-
