This species is founded on the anterior end of a premaxillary bone; in form not unlike _O. Fittoni_. It is 5/8ths of an inch wide; the lateral margins approximate very slowly, and in front it appears to be truncated. It is an inch and a quarter long, and in that space were on each side six large round teeth, almost as close together as they could be, five on the palate and a pair in front. The terminal two are no wider apart than the rest, and point more forward. A moderate, sharp, median ridge descends in the flattened palate, making its lateral halves a little concave. The front termination of the palate is slightly reflected upward. The jaw, which is 1/2 an inch deep behind, tapers to its termination more rapidly than does _O. Fittoni_. The flat sides similarly converge, and form a well-rounded ridge, which does not get blunter in front. From their close approximation, it results that the tooth-sockets are entirely above the palatal surface, so that they are better seen from the side of the jaw than from the palate. It is a clearly marked species, as well distinguished from _O. Fittoni_ by the closeness of its teeth, as _O. Sedgwicki_ is from _O. Cuvieri_. XVI. Ornithocheirus denticulatus (Seeley). Case. Comp. Series. Tablet. =J= _c5_ 28 1 This is a species which can only be confounded with O. polyodon. It is a fragment of premaxillary bone 1-3/4 inch long, fractured through the seventh socket. It differs from O. polyodon in having larger teeth, which are wider apart, look more downward, have a narrower palatal interspace between each pair, and a rostral keel, which is more compressed from side to side behind and from above downward in front, and makes a greater angle with the palate. The sockets are more uniform in size and closer together than usual, the second and third pairs being but slightly larger than the others; all are broadly elliptical. The palatal keel becomes sharp and prominent behind the fourth sockets. Behind the second pair of sockets the height of the jaw is nearly 7/16ths of an inch, behind the fourth sockets the height is 10/16ths of an inch; the distance between these points is about 10/16ths of an inch. XVII. Ornithocheirus crassidens (Seeley). Case. Comp. Series. Tablet. =J= _c1_ 2 2 This is a fragment of a ?premaxillary bone, fractured behind through the socket for the fourth tooth. It approximates to O. colorhinus, but differs chiefly in the nose not extending in front of the first pair of teeth; in there not being any lunate area above the first pair of teeth; in there being but one tooth in front, which is relatively large; in the socket for the fourth tooth being quite close to that for the third tooth, and in the palatal sockets looking much more outward. The nose also appears to be better rounded.