60 Field Columbian Museum — Geology, vol. II. 



sphenoid. It would seem that there could be no further question as 

 to the character of these vacuities — simply fortuitous openings — 

 separated by a remarkably persistent, well-ossified parasphenoid, 

 invariably found in all plesiosaurs, but never in their nearest allies, 

 the turtles and nothosaurs. In most of the plesiosaurs in which the 

 palate is known, the openings are situated more nearly upon the 

 plane of the palate, and, though somewhat variable in shape, are 

 always of moderate or considerable size. In this species, however, 

 they are at the bottom of a well-marked, rather deep fossa, with well 

 defined lateral walls and a sloping posterior roof. 



These foramina in the plesiosaur skull were first thought to be 

 the nares by Owen, who, however, confounded the anterior part of 

 the pterygoids with the palatines. Huxley, who was also not clear 

 about the palatines, suggested that the real internal nares were smaller 

 openings situated more anteriorly. Sollas (1. c.) discussed the matter 

 more at length and reached the conclusion that the real internal nares 

 were situated far in front, between the premaxilla and vomer, with 

 the palatines probably entering into the posterior border. Andrews 

 has accepted this location of the nares, and has figured and described 

 the openings in three genera of the plesiosaurs, always bounded by 

 vomer, palatine and maxilla. In DolichorJiyncJiops osborni, however, 

 as seen from the figure and descriptions, these openings can only be 

 situated between the vomers and palatines and at some distance 

 from the maxillae. In my description I accepted these orifices as the 

 true nares, though greatly astonished at their minute size, and 

 although they correspond with similar foramina between the vomers, 

 in the mosasaurs. 



If we are to seek for the nares in their present specimen else- 

 where than in the openings I have described it must be far forward, 

 perhaps in precisely the position assigned to them by Sollas. In all 

 the known forms, with this interpretation, they would be in front of 

 the external nostrils, in the present species far in front. What 

 possible combination of circumstances would have caused the recession 

 of the external nostrils to a place so close to the orbits without 

 affecting the position of the internal openings? I certainly suspect 

 that in this species at least the openings between the pterygoids are 

 the rt-al internal nares. As to the character of the separating element 

 I am forced to the conclusion that Andrews has reached, that it is 

 the parasphenoid. If the element in front called the vomers are 

 rc-ally those bones, and there could seem to be no doubt that they are, 

 then- is nothing else left, save possibly the turbinated bones. 

 The slender bone in precisely similar position in the ichthyosaurs 



