318 G. F. Eaton — Characters of Pteranodon. 



Art. XXYIII. — Characters of Pteranodon (Second Paper J : 

 by G-. F. Eaton. (With Plates XIX and XX.) 



Brief notices of some of the characters of Pteranodon Marsh 

 were published in this Journal in July, 1903. A restoration of 

 Pteranodon longicejps is now about to be installed at St. Louis, 

 which has been prepared under my direction as the contribution 

 of the Department of Vertebrate Palepntology of the Yale 

 Museum to the University's exhibit at the Louisiana Purchase 

 Exposition. It is therefore advisable to describe such additional 

 characters of Pteranodon as are manifest in the restoration. 



A half-tone engraving of this restoration appears as Plate 

 XIX. 



The Sclerotic Circle. 



The sclerotic circle is composed of twelve thin plates of bone 

 arranged with overlapping edges, so as to form a hollow trun- 

 cate cone similar in shape to the avian sclerotic circle. Plate 

 XX, figure 1, shows the arrangement of these plates in the left 

 orbit of a large head of Pteranodon. By removing the matrix 

 from under the left side of the skull, which was crushed later- 

 ally, the circle was exposed pressed inward against the inter- 

 orbital septum and with the component plates little disturbed 

 from their normal position. 



Professor Williston* refers to the sclerotic circle of the allied 

 genus Nyctosaurus (Nyctodactylus) in these words : " It had 

 a ring of thin, large sclerotic plates, which were preserved in 

 displaced positions. The separate plates were not united by 

 imbrication, as in the mosasaurs." The chapter on the Ptero- 

 sauria in the new edition of Zittel's Paleontology, 1902, as 

 revised by Professor Williston, contains no description of this 

 structure in either Pteranodon or Nyctosaurus. Oddly enough, 

 in this revision, it is Pteranodon that is credited with a scle- 

 rotic circle, and not Nyctosaurus in which Professor Williston 

 observed the structure. 



The Vertebrae. 



The most important note to be made here concerns the ver- 

 tebral formula, which I have now determined. I have figured 

 and described in this Journal (July, 1903) the series of verte- 

 brae which are anchylosed together to support the ilia. Fur- 

 ther investigation has shown the number of presacrals attrib- 

 uted to Pteranodon by previous writers to be incorrect. 

 Instead of eight cervicals, as given by Professor Williston, 

 there are in reality nine. In the dorsal series are included 



* Journal of Geology, vol. x, p. 528, 1902. 



