On the Osteology of Nyctosaurus. 135 



slightly removed. The length of the series is about fifty millimeters, 

 showing that five vertebrae are associated in it, and that the protruding 

 one is the fifth. Whether the fourth and fifth are both suturally united 

 in the notarium cannot be said, but in all probability the fifth at least is 

 free, since its convexity shows it to be of the nature of the following ones, 

 and because one of the small posterior ribs seems to have been articulated 

 with it. The sixth, seventh, eighth, and ninth vertebrae are nearly in 

 relation with each other, behind the sternum, lying upon their dorsal 

 side, but are pushed somewhat to the left. They are cylindrical in cross- 

 section, with smooth, evenly concave sides and inferior border, with a 

 deep cup and a prominent ball. They are a little longer than broad, of 

 nearly equal length, though a little more slender posteriorly. The ante- 

 rior zygapophyses extend in front of the cup. The elongated and slender 

 diapophyses arise high up on the arch from near the anterior part of the 

 vertebra, and are directed horizontally outward. These vertebra? are quite 

 similar to those of Pteranodon, and are doubtless quite like that figured 

 by Seeley in his Dragons of the Air, p. 86, Fig. 26. The last dorsal (or 

 first sacral) (PI. XLI, Fig. 1, dv), the tenth back of the neck, is flat on its 

 inferior surface, and its transverse process I think arises from the centrum 

 as in Pteranodon. It is firmly united with the sacrum by suture in both 

 genera, and is quite as properly counted with the sacrum as with the 

 dorsal or lumbar vertebrae. It is probable that its transverse process 

 unites with, or reaches to, the anterior projection of the ilium, as seems 

 also to be the case in Pteranodon. 



The position in which the skeleton is lying indicates that the right 

 coraco-scapula and the pelvis are in the positions in which they were as 

 regards each other while yet held together by the ligaments. The right 

 arm, falling across the abdomen, has caused a slight dislocation of the 

 dorsal vertebrae, the notarium held by the ribs has been turned somewhat 

 obliquely, and the sternum has settled down a little to the left. The 

 ends of the scapulae, however, are nearly in the relative position to each 

 other which they must have held during life, and the axis of the sacrum 

 is in line nearly with the presternum. 



Now, by bringing all the vertebrae back into a straight line, the ten 

 vertebrae fill the entire space between the neck and the true sacrum, 

 proving almost incontestably that there were neither more nor less than 

 ten, a number found in no other reptiles except the turtles and Pareia- 

 saurus; indeed, if we call the last a sacral, then there are fewer presacral 

 vertebrae in Nyctosaurus than in any other known reptile. 



The sacrum proper, as described below, is composed of six vertebrae, 

 the lines of sutural union of which are clearly visible in the specimen. 



Four caudal vertebrae are preserved, lying close to the proximal end 



