50 Trof, 0. C. Marsh — On Birds tvith Teeth, 



premaxillary bones supported teeth, or were covered with a horny 

 beak, cannot be determined from the present specimen. 



The scapular arch and the bones of the wings and legs all conform 

 closely to the true avian type. The sternum has a prominent keel, 

 and elongated grooves for the expanded coracoids. The wings were 

 very large in proportion to the legs, and the humerus had an ex- 

 tended radial crest. The metacarpals are coossified, as in recent 

 birds, thus differing widely from those of Arcliceo'pteryx. The bones 

 of the posterior extremities are slender, and resemble those of some 

 aquatic birds. The centra of the vertebrse are all biconcave, the 

 concavities at each end being distinct, and nearly equal (Plate II. 

 Figures 3 and 4). The sacrum is elongated, and made up of a large 

 number of coossified vertebrge. Whether the tail was elongated or 

 not cannot at present be decided. 



The jaws and teeth of this species show it to have been carnivo- 

 rous, and it was probably aquatic. Its powerful wings indicate that 

 it was capable of prolonged flight. 



Another Cretaceous bird (Apatornis celer, Marsh), belonging ap- 

 parently to the same order as Ichthyornis, was found by the writer 

 in 1872 in the same geological horizon in Kansas.^ The remains 

 preserved indicate an individual about the same size as Ichtliyornis 

 disiiar, but of more slender proportions. The vertebra are biconcave, 

 and there were probably teeth. 



The most interesting bird with teeth yet discovered is perhaps 

 Sesperornis regaJis, a gigantic diver, also from the Cretaceous of 

 Kansas, and discovered by the writer in 1870. The type specimen, 

 which was found by the writer in 1871, and described soon after, 

 consisted mainly of vertebree and the nearly complete posterior 

 limbs, all in excellent preservation.^ 



A nearly perfect skeleton of this species was obtained in Western 

 Kansas by Mr. T. H. Eussell and the writer in November, 1872, 

 during the explorations of the Yale College party, and several other 

 less perfect specimens have since been secured, and are now in the 

 Yale Museum. These various remains apparently all belong to one 

 species. 



The skull of Sesperornis has the same general form as that in 

 Colymbus torquatus, Briin., but there is a more prominent median 

 crest between the orbits, and the beak is less pointed. The brain 

 cavity was quite small. The maxillary bones are massive, and 

 have throughout their length a deep inferior groove which was 

 thickly set with sharp, pointed teeth. These teeth had no true 

 sockets, but between their bases there are slight projections from 

 the sides of the grooves. (Plate II. Figure 6.) The teeth have 

 pointed crowns, covered with enamel, and supported on stout fangs. 

 (Plate II. Figure 9.) In form of crown and base, they most resemble 

 the teeth of Mosasauroid reptiles. The method of replacement, also, 

 was the same, as some of the teeth preserved have the crowns of 

 the successional teeth imj)lanted in cavities in their fangs. The 



^ Silliman's American Journal, vol. v. p. 74, Jan. 1873. 

 2 Silliman's American Journal, vol. iii. p. 360, May, 1872. 



