Geology. 149 



Pteranodon ingens, P. longiceps, and P. occidentalism were suffi- 

 ciently complete to form the immediate basis for research. No 

 attempt is made to amplify specific descriptions and the author 

 plunges at once into the osteology of the genus, during which 

 certain details of specific distinction are mentioned. 



The skull shows a complete obliteration of sutures, and in its 

 extremely narrow proportions and the extension of the great supra- 

 occipital crest and of the toothless jaw is utterly unique among 

 vertebrates. The curious spirally grooved jaw articulation, resem- 

 bling that of the pelican, though developed to a higher degree, 

 the effect of which is to bow outward the rami of the lower jaws, 

 together with the apparent presence during life of a gular pouch, 

 is suggestive of fish-eating habits. The supraoccipital crest is 

 compared with that of Phalacrocorax, Chelydra, and Chamaeleo 

 and its initial development is accounted for by the necessity 

 for increased origin of the powerful temporal muscles. How 

 far these spread over the crest is not ^nown, but it is supposed 

 that a secondary function of the crest must have arisen to account 

 for its extreme development. In this connection a counterpoise 

 for the long jaws and the effect of the crest as a vertical aero- 

 plane cannot be entirely disregarded. 



The cervical vertebrae, while apparently massive, are of 

 extreme lightness of construction. As in certain birds the ante- 

 rior dorsals are fused into a rigid notarium, then, after an inter- 

 val of three or four free vertebrae, the long synsacrum of nine 

 or ten codssified vertebrae appears, again very bird-like in struc- 

 ture. The tail was evidently very short and of little value in 

 flight. 



The shoulder girdle is very massive, the scapulae articulating 

 with a very distinct facet on either side of the fused dorsal spines 

 of the notarium. There is a powerful sternum, somewhat keeled 

 for the origin of the great muscles of flight. 



The limb bones have been well described by earlier authors 

 but note is taken of the various ways in which they may be 

 modified by the crushing to which they have been subjected and 

 which renders specific distinctions based upon these elements of 

 little value. The phalangeal formula of the manus is correctly 

 stated for the first time and shows the ordinary reptilian sequence 

 of bones. 



Two admirable restorations are given which are, however, 

 composite, in that elements from more than one species had to be 

 used in their construction. One shows the animal from the side, 

 the other from below with wings broadly expanded as in the 

 plaster replicas preserved in the Yale and 17. S. National Museums 

 and in the British Museum of Natural History, all of which were 

 made under Dr. Eaton's supervision. 



Dimensions of the various specimens under consideration are 

 given, the most interesting being the alar expanse, conservatively 

 estimated in that the bones were given their natural angulation. 

 They range from Pteranodon sp. (Cat. No. 1181) with 3-390" 1 



Am. Jour. Sci.— Fourth Series, Vol. XXXI, No. 182.— February, 1911. 

 11 



