S6 G. F. Eaton — Char^act'ers of Pteranodon, 



the avian sacrum, chose the intervertebral foramina as the 

 best criteria for distinguishing true sacrals from sacro -dorsals 

 and uro-sacrals. In the present fossil specimen there are, of 

 course, no nerves to serve as guides, but I hope to show in a 

 subsequent paper that vertebrae 5, 6, and 7, which clearly form 

 a natural division, are the true sacrals. Vertebra 4 may prove 

 to be the homologue of the last lumbar vertebra in the sacrum 

 of recent birds. In closing I should like to state, with due 

 apologies to Prof. Lydekker, that the "parallel" between the 

 sacrum of Pteranodon and that of recent birds is striking, 

 though I have no desire to ^^ostulate "converging lines" of 

 structure and descent. 



Paleontological Laboratory, Yale University Museum, 

 June 8, 1903. 



EXPLANATION OF PLATES. 

 Plate VI. 



Figure 1. — Restoration of skull of Pteranodon. 



True outline of sagittal crest is shown by continuous line. 



Marsh's restoration of sagittal crest is shown by dotted line. 



One-sixth natural size. 

 Figure 2. — Enlargement of Williston's diagram of skull of Pteranodon. 



Approximately one-quarter natural size, 



Plate YII. 



Figure 1. — Pelvis of Pteranodoyi] side view. 

 Figure 2, — " " ; top view. 



Figure 3, — " *' ; bottom view. 



All three figrures are one-half natural size. 



