WILLISTON: RESTORATION. OF ORNITHOSTOMA (PTERANODON). 37 
For that reason I have yet failed to determine some of the species 
described previously. O. iugens is, however, more easily recog- 
nizable from the size alone, in which it seems very constant. 
Among the material of this genus in the University I have recog- 
nized four species, based partly upon size, partly upon structural 
differences. Such differences are found in the shape of the hu- 
merus, the terminal wing phalanx, the relative length of the bones, 
etc, 
The material which I have referred to O. ‘ngens includes some 
twenty specimens, which have furnished all parts of the skele- 
ton save some of the cervical and dorsal vertebre, the pelvis and 
the larger part of the skull. The pectoral girdle and anterior ex- 
tremity, with the exception of the terminal phalanx, together with 
the complete leg, are from one specimen—the vertebra from an- 
other. The pelvis is drawn from a specimen of another species, 
comprising the larger part of the skeleton. The resemblances of 
the skeleton throughout are so great that there can be little doubt 
that the pelvis would be equally indistinguishable, save by size. 
It is unnecessary to add that its size in the drawing has been made 
proportional to that of the other bones. Of the skull, the larger 
part of the lower jaws and some of the posterior portions are alone 
available in this species, and the remainder is taken from one be- 
longing toa smaller form. I have assumed that this latter spec- 
imen is of another species, but the difference in size is all that | 
have so far been able to discover. 
The number of dorsal vertebra can not be determined. The re- 
lative positions of the pectoral girdle and leg in several specimens 
show pretty conclusively that the trunk could not have been longer 
than has been figured. 
Altogether the skeleton of Ornithostoma presents some very re- 
markable characters. I believe there is no other reptile in which 
prosthenic features are carried to as high a degree as in this. The 
disproportion between the fore and hind extremities is almost ludi- 
crous. The pelvis is exceedingly small, the legs not only small 
but weak in all respects. That the animal could have stood upon 
its feet free on the ground I do not believe possible. The neck 
vertebrae are relatively stout, but the neck was not remarkably 
elongated, to carry sucha head as the animal possessed. Further- 
more the remarkable mode of articulation of the neck and anterior 
dorsal vertebra seems to indicate a restricted range of torsion, 
though tolerably wide sagittal flexion. The occurrence of the re- 
Mains of the large species in strata evidently formed remote from 
