Prof. II. G. Seeley on the Ornithosaurian Pelvis. 255 



The osseous resemblances between these groups of animals may 

 be better summarized in a diagram (fig. 16) *, where the letters 

 I, Is, P, pp, stand respectively for ilium, ischium, pubis, and 

 prepubis in the several groups of animals, and the lines drawn 

 from one group to another show the resemblances between 

 the bones. From this it would appear that the relations of 

 the Ornithosauria seen in the pelvis are closer with extinct 

 than with the existing groups. This conclusion is of some 

 importance, since the Ornithosauria may be associated with 

 Birds from the resemblances in their brains, and associated 

 with Birds and Saurischia from possessing a pneumatic skele- 

 ton, though it is less developed in the latter group than in the 

 others. These resemblances, when better evidenced by the 

 discovery or description of specimens which show the bones 

 in complete natural connexion, may justify the linking of 

 these orders together in a natural alliance (the Ornitho- 

 morpha) expressive of their common origin. 



The Classification of the subclass Ornithosauria which 

 seems to me best supported by facts is the following 

 division : — 



Order 1. ORNITHOCHEIROIDEA. 

 Family Ornithocheiridae. 

 Family Pteranodontidge. 



Suborder 2. Pterodactylia. 

 Family Pterodactylidse. 



Order 3. PTERODERMATA. 

 Family Dimorphodontida?. 

 Family Rhamphorhynchidae. 



Here the Orders are founded upon the organs of flight, 

 brain, skull, and pelvis ; the Families in the first Order are 

 based provisionally on the dentition, and in the third Order 

 upon pelvic characters. 



* The central circle is provisionally given to the Aristosuchia, which 

 have the skeleton pneumatic, pubes directed forward, anchylosed to the 

 prepubes, which are anchylosed together. No posterior limb to the 

 pubis. 



18* 



