R EMAINS of birds are among the rarest of fossils, and few have been described save from the more recent formations. With the exception of Archceopteryx from the Jurassic, and a single species from the Cretaceous, no birds are known in the old world below the Tertiary. 2 In this country, numerous remains of birds have been found in the Cretaceous, but there is no satisfactory evidence of their existence in any older formation, the three-toed footprints of the Triassic being probably all made by

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... Dinosaurian reptiles. The Museum of Yale College contains a large series of remains of birds from the Cretaceous deposits of the Atlantic coast and the Eocky Mountain region, thirteen species of which have already been described by the writer. The most important of these remains, so far as now known, are the Odontornithes, or birds with teeth, and it is the object of the present communication to give some of the more marked, characters of this group, reserving the full description for a memoir now in course of preparation. The first species of birds in which teeth were detected was Ichthyornis dispar, Marsh, described in 1872. 3 Fortunately the type specimen of this remarkable species was in excellent preservation, and the more important portions of both the skull and skeleton were secured. These remains indicate an aquatic bird, fully adult, and about as large as a pigeon. The skull is of moderate size, and the eyes were placed well forward. The lower jaws are long, rather slender, and the rami were not coossified at the Bymphysis. In each lower jaw there are twentyone distinct sockets, and the series extends over the entire upper margin of the dentary bone (Plate II. Figures 1 and 2) . The teeth in these sockets are small, compressed and pointed, and all are directed more or less backward. The crowns are covered with nearly smooth enamel.