158 Field Columbian Museum — Geology, Vol. II. 



young of P. ingens, as is not likely, then we have at least three distinctly 

 different species of the genus, perhaps a fourth in P. comptus. 



A much more interesting question is : What relation do the genera, 

 Nyctosaurus, Ornithocheirus, and Pteranodon (Omithostoma) bear to each 

 other and to Pterodactylus ? 



The classification which has hitherto seemed the best to display the 

 relationship of these forms is the following : 



Suborder Pterodactyloidea. Tail short; wing metacarpal, at least as 

 long as the bones of the antebrachium; fifth digit of pes vestigial, with- 

 out phalanges. 



Family Pterodactylidae. Scapula not articulating with supraneural 

 facet. 



Genus Pterodactylus. Teeth present. 



Genus JVyctosaurus. No teeth. 



Family Ornithocheiridae. Scapula with an articular facet united with 

 neural facet of the notarium. 



Genus Omitkocheirus. Jaws with teeth. 



Genus Pteranodon {Ornithostoma). Jaws without teeth. 



However, a better knowledge of the genus JVyctosaurus convinces 

 me that its relationship is closer with Ornithocheirus than with Pterodacty- 

 lus; that it has gone much further in specialization in the same direction 

 with Ornithocheirus and Pteranodon. Very little now remains to be 

 known of the osteology of both these genera, and not much of Ortii. 

 thocheirus . Their characters as a group may be summed up as follows. 

 While some parts of the skeleton of Ornithocheirus are yet unknown, I 

 am confident that future discovery will produce nothing very discrepant. 



Ornithocheiridoz. Head elongate, slender; no antorbital vacuity; 

 internal nares large; eight cervical, ten dorsal {Pteranodon?}, six 

 sacral, and ten to twelve caudal vertebrae present, the last dorsal co-os- 

 sified with the sacrum; first three or four dorsal vertebrae united into a 

 notarium, with stout, anchylosed ribs articulating with the sternum; pos- 

 terior dorsal ribs very slender, single-headed, and nearly straight; three 

 or four pairs of flattened V-shaped ventral ribs present. Ilium much 

 elongated; ischio-pubis with an obturator foramen; prepubes band-like, 

 co-ossified, with an anterior, flattened projection on eaCh side. Coraco- 

 scapula with only a slight projection below the glenoid cavity, co-ossified 

 in the adult; scapula but little longer than the coracoid, not narrowed 

 distally. Three carpals present; forearm much longer than humerus; third 

 and fourth metacarpals very short, pointed proximally, not articulating 

 with carpus; second metacarpal thread-like proximally; fifth metacarpal 



