On the Osteology of Nyctosaurus. 153 



altogether reminding one very much of similar tendinous ossifications 

 in the legs of many birds. 



A number of other slender, rib-like, more or less fragmentary bones 

 are observed scattered about the slab near the body of the specimen, 

 of which I am not at all certain, though I suspect that some of them 

 are ventral ribs, perhaps attached during life to the extremity of the 

 flat parasternal structures already described. One of these bones, lying 

 by the lateral margin of the sacrum is about forty millimeters in length 

 and is gently curved. It is flattened at one end, measuring nearly three 

 millimeters in width, cylindrical at the other, and not more than one 

 millimeter wide. Another, lying back of the pelvis, of about the same 

 length is also slightly curved, one millimeter wide at one end and 

 about three-tenths of a millimeter in width at the other end. There 

 are also parts of several other bones which seem to be similar to these. 



SYSTEMATIC POSITION. 



Three specimens ascribed to Nyctosaurus are now known — the type 

 described briefly by Marsh, the one in the University of Kansas Museum 

 described by me in 1892, and the present one. Marsh must have known 

 more than one specimen, however, in which additional specimens he 

 later recognized the essential generic characters. The three specimens 

 differ materially in size, that described by Marsh being the largest, and 

 the Kansas University specimen the smallest. In the smallest speci- 

 men the coracoid and scapula are still distinguished by a separable 

 suture. Furthermore, the separated arches of the dorsal vertebrae, and 

 the distinction of the elements of the atlas all indicate a young animal. 

 On the other hand, the present specimen has all of its sutures obliter- 

 ated, except that between the atlantal intercentrum and the axial inter- 

 centrum, characters which may be ascribed to an adult condition. Among 

 the characters given by Marsh, is the separated coracoid and scapula, 

 but I suspect that this was derived from a smaller specimen than the 

 one which he originally named Pteranodon gracilis. I do not think 

 that the absolute differences in size are sufficient to separate the speci- 

 mens specifically, in that we know that similar differences are ascribed 

 to other pterodactyls by some authors. In order, however, to make the 

 comparative differences between these specimens clearer I have reduced 

 them to a common standard, using the humerus as 100 in each. In addi- 

 tion, I give like comparative measurements of certain species of Pterodac- 

 tylus, derived from figures given by Zittel: 



