Length of femur 75 Diameter of head of femur 5 Diameter of femur through condyles 12 Length of pteroid bone 88 The principal dimensions of this species can be got at with considerable certainty. Although two of the wing-phalanges and the bones of the foot are wanting, yet the relative proportions of those present agree so closely with those of the corresponding bones in _Pteranodon_, that there can be but little possibility of error in assuming the same proportions for the missing ones. The position of the ilium and femur, as also the ribs, show that they hold their natural relations to the pectoral arch. The tail, alone, can not be got at. Extreme expanse of wing-bones 2400 mm. 7 ft. 10 in. Expanse of wings in life, approximated 2000 6 6 Length of head, estimated 150 6 Length of neck 128 5½ Length of trunk 165 6½ Length of leg and foot, outstretched 275 11 But one species has been described from the American Cretaceous smaller than the present one, _Pteranodon nanus_ Marsh, in which the expanse of wings is given as not more than three or four feet. In this estimate the author is certainly in error. The size of the humerus, as given, is rather more than three-fourths that of the present species, and the expanse, hence, must be nearly five feet in life, or six feet as the bones lie outstretched. As regards the specific determination of the present specimen, there must necessarily be some doubt until the species already named have been recognizably described. But three of the existing species can be taken into account, _N. gracilis_, _P. comptus_ and _P. nanus_. That it can not be the last, has already been shown. In size, it agrees well with _P. comptus_, but the other characters throw no light upon the identity. The measurements given of the type specimen of _N. gracilis_ show the size to be materially greater,—a character, however, of subordinate value—greater slenderness, and a relatively shorter first wing-phalanx. The relative lengths of wing-metacarpals, wing-phalanx and ulna in _N. gracilis_ and the present specimen may be expressed as follows: Length of wing-metacarpal 100 100 Length of first wing-phalanx 115.6 119.5 Length of ulna 62.3 60.4 It will be seen that not a single character has yet been given to distinguish the genus from _Pterodactylus_, and it is not at all impossible that it may prove to be the same; its location among the _Pteranodontidae_ rests solely on the assumed absence of teeth, and that is a character yet wholly unknown.