412 MK. B. W. H00LEV OX THE [June igijy 



longitudinal ridge on the palate. The typical dentigerous pre- 

 maxillse of the Cambridge Greensand in the Sedgwick Museum,, 

 although belonging to several genera, have been included in the 

 genus OrnitJiocJieirus, and endowed with the characters obtained 

 from the fragments of bones ; and also, on the discovery of the 

 edentulous jaw, Ornithostoma with those pertaining to the American 

 toothless forms. Thus Prof. "Williston * remarks that not much 

 remains to be known of the osteology of OrnitJiocJieirus; whereas, 

 in reality, nothing is known except the tip of the snout. Again , 

 Dr. Plieninger, 2 following Williston, gives this classification : — 



Family: Orni th och eiridae. Orbit, preorbital, and nasal opening com- 

 pletely separated. Early dorsal vertebrae blended into the so-called 

 notarium. 

 Sub-Family : Ornitbocheirinae. Scapula in union with the notarium. 

 Sagittal crest to skull. 

 Genera : Ornithochcirus. Toothed. 

 Pteranodon. Toothless. 



The only character obtained from the genus OrnitJiocJieirus is 

 ' toothed,' the family and sub-family characters are those of tlTe 

 genus OmitJiostoma (Pteranodon). 



OrnitJiodesmus is also generically distinct from OrnitJiocJieirus 

 sagittirostris (Owen). 3 The form of the teeth, the interspaces, 

 between them, their insertion in distinct alveoli with highly- 

 raised rims, the length of the alveolar teeth, and the form of the 

 rami, are quite different. 



OrnitJiodesmus appears to have descended from a sub-order which 

 should include Scajphognathus and DimorpJiodon, necessitating the 

 withdrawalof these two genera from the Rhamphorhynchidae, and 

 the formation of a new sub-order. 



The three entirely varied phases of development in the skulls 

 of Ornithosauria give a ready means of division into three sub- 

 orders, as follows : — 



Sub-Order: Scaphognathoidea. 



Skull an open framework of bone, all fossae very large. Nasal and 

 preorbital vacuities separated. Concave lizard-like occiput. 



Sub-Order : Pterodactyloidea. 



Half the area of the skull encased in bone, all fossae moderately large. 

 Nasal and preorbital vacuities confluent. Convex bird-like occiput. 



Sub-Order : Ehamphorhynchoidea. 



Skull nearly encased in bone, all fossae considerably reduced. Nasal 

 and preorbital vacuities separated. Flat occiput. 



In regard to the remainder of the axial and appendicular 

 skeleton, the type-specimens are mostly crushed, fragmentary and so 



1 ' Osteology of Nyctosaurus, &c.' Field Col. Mus. Publ. 78, Geol. Ser. vol. ii, 

 No. 3 (1903) p. 158. 



- 'Die Pterosaurier der Juraformation Sckwabens-' Palaeontographica, 

 .vol. liii (1907) p. 313. 



3 'Foss. Kept. Mesoz. Form." pt. i (Monogr. Pal. Soc.) 1874, p. 3 & pi. ii. 



