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.
The material now in the museum permits a fuller discussion of the relations and characters of this group of reptiles than has been hitherto attempted. Originally, they were described as constituting a new order, a view still held by its author and no one else. Lydekker, in his Paleontology and Catalogue gives them a subordinal value; Zittel only a family value, though expressing doubt as to their subordinal rank.
It seems very probable that the genus Nyctodactylus has no teeth in the jaws; it agrees in every other respect with the genus Pterodactylus, so far as known. If the genus has teeth it must be united with Pterodactylus. Now, in not a few species of this genus, the teeth are confined to the anterior end of the jaws, and their entire absence, unaccompanied by other structural differences, will hardly constitute an order, or even family.