glass slide. It showed large vacuities, especially at the attached base, filled with pyritic matter; and in the body of the tooth this matter occupied and demonstrated part of the vascular canals. These show chiefly a longitudinal course (Pl. XVII. fig. 1, a), or in the direction of the tooth's axis, united by short cross branches of minor diameter (b), including oblong spaces (c). The general arrangement being thus reticulate as in bone, the vascular substance not having filled a basal conical cavity, like the dentinal pulp of a true tooth, a large proportion of the osseous tissue of the process was preserved, showing, under a magnifying power of 250 diameters (fig. 2), the bone-cells. These have the proportions of length and breadth characteristic of the bones of birds, and also of Pterodactyles. Many of the bone-cells were in the direction of the long axis of the process, as at a, a (fig. 2), and averaged in length 1800 of an inch; others, nearer the vascular canals, were arranged in a direction at right angles to the long axis of the process, as at b, b, ib.: these indicated a short or transverse diameter of the cell of 13000 an inch. The canaliculi from the bone-cells were obliterated. Thus the microscopic test, in the degree in which I have been enabled to apply it, shows the osseous characters of the tooth-like processes, and adds to the probability of the conclusion drawn from the external vascular markings, that they were sheathed by hollow processes of the horny beak in the living bird.
With the exception of the better-preserved canaliculi in the microscopic sections of the bone-tissue of a fossil femur of a bird from Sheppey, figured by Quekett[1], the size and shape of the bone-cells are much alike in that and the present fossil from the same formation and locality.
I conclude therefore that Odontopteryx, like Archæopteryx, was a warm-blooded feathered biped, with wings, and, further, that it was web-footed and a fish-eater, and that in the catching of its slippery prey it was assisted by this pterosauroid armature of its jaws.
The cretaceous fossil skull, affirmed by Professor O. C. Marsh to be that of a bird with teeth, and which he proposes as the type of a genus under the name Ichthyornis, also of an order which he calls "Ichthyornithes," and of a new subclass of birds under the name "Odontornithes" or "Aves dentatæ"[2], differs from the Sheppey fossil in having "the eyes placed well forwards," in having "the lower jaw long and slender," in having "the teeth quite numerous and implanted in distinct sockets," and in the size and shape of such teeth. They are described as being "small, compressed, and pointed, and all alike," or "similar." "Those in the lower jaw number about twenty in each ramus, and are all more or less inclined backward." "The maxillary teeth appear to have been equally numerous and essentially the same as those of the mandible "[3].
