On the Osteology of Nyctosaurus. 151 



extending further, is much less in extent. The inner distal articular sur- 

 face is the larger, and is separated from the inner surface by a distinct 

 ridge, especially posteriorly. 



Tibia. PI. XLIV, Fig. 3. The tibia is a slender, straight bone, mod- 

 erately expanded at the upper extremity. The margin of the articular 

 surface above is nearly transverse to the longitudinal axis. The width 

 contracts chiefly at the expense of the posterior margin to the lower part 

 of the upper fourth of the bone, the shaft below being of nearly uniform 

 width. The trochlear surface at the distal extremity is pulley-shaped, 

 covering about half of a circle, perhaps more, and has a moderately 

 deep groove. The sutural union between the tibia proper and the prox- 

 imal tarsal bone, or bones, is entirely obliterated. The bones of the two 

 sides are compressed in different positions, the left one from the side, the 

 right one from nearly in front ; the width above is considerably greater 

 in the former than in the latter, indicating but comparatively little ex- 

 pansion of the upper part from side to side. 



There is no trace of any fibula, either in the preserved remains or in 

 any tibial articulation. 



MEASUREMENTS OF TIBIA. 



mm. 



Length T 133(132) 



Width above '. 15 ( 11) 



Width of shaft at upper end of middle third-- 7 ( 6) 



Width, lower third 6( 6) 



Antero-posterior diameter of trochlea 6( 6) 



Foot. But a single metatarsal and one phalange are present in this 

 specimen. These, however, agree so well with the corresponding bones 

 of Pteranodon that I doubt not the foot was quite similar to that of the 

 former genus. This metatarsal is expanded at its proximal end and 

 gently convex on the trochlear end. It measures 35 mm. in length, 2 mm. 

 in width at the upper fourth and 4 mm. at either extremity. The bone is 

 compressed from side to side. The phalange, flattened on the side, has 

 a length of 14 mm. The distal end has the extremity convex, its chord 

 rectangular to the long axis of the bone ; its width is 3 mm. The 

 proximal end is truncated or gently concave ; its width is about 4 mm. 

 The shaft in the middle is scarcely narrowed from the proximal end. I 

 repeat here, briefly, the description of the foot of Pteranodon, from my 

 paper in the Kansas University Quarterly, vol. vi, page 50, with some 

 changes. 



The first four metatarsals are very slender, straight, and contiguous 

 with each other, each having a flattened proximal articular surface and 

 a rounded trochlear distal extremity. The metatarsal of the fifth toe is 



