398 MR. R. W. HO0LEY ON THE [Julie I913, 



IV. MORPHOLOGY, AND COMPARISONS WITH OTHER SPECIES. 



The region between the snout and the occiput is highly modified, 

 beyond all analogy with any known skull of the recent or fossil 

 Iteptilia. A straight dorsal outline of the beak is also found in 

 Pterodactylus, Campylognathus, lihamphorhynchus, Omithostoma, 

 and Nyctosaurus. In this respect Ornithodesmus varies from Dimor- 

 phodon and Scaphognatlms crassirostris, where the beak is boldly 

 convex, and approaches Sc. purdoni, where the beak has only a 

 moderate convexity and is much more elongated. The concave 

 reptilian occiput also closely resembles that seen in this species, 

 and reminds one vividly of the Lacertilia, as, for example, Lacerta 

 ocellata and Varanus varius, and the Ehynchocephalian Hatteria 

 punctata. 



The Nares. 



The nares differ from those of other species in their greater area 

 and close proximity to the extremity of the muzzle, although their 

 position is posterior to the teeth. They are large, and situated 

 near the end of the snout in Dimorphodon ; but they are nearly 

 vertical, and occur above the central lateral alveolar border. In 

 Scaphognatlms crassirostris they are smaller, and have the same 

 inclination and position as in Dimorphodon. Like features obtain 

 in Sc. purdoni, but they are farther from the tip of the jaws, and 

 by their continuation behind the teeth approximate to Ornitho- 

 desmus latidens. In Rhamphoryhnchus gemmingi they are much 

 reduced in dimensions, and terminate before reaching the last teeth. 

 All these agree with 0. latidens in having the nares separated 

 from the antorbital fossa? by a long bar. In Pterodactylus antiquus. 

 Pt. kochi, and Pt. suevicus, the nares occur some distance behind 

 the teeth, and are confluent with the antorbital vacuities. In 

 Omithostoma and Nyctosaurus they are very small. 



The Antorbital Vacuity. 



The antorbital vacuity is greater in extent than, and dissimilar 

 in form to, that of any other species. 



The Antorbital Vacuity No. 2. 



Xo Ornithosaur has anything approximating to the remarkable 

 infra-orbital fossa of Ornithodesmus latidens. The extraordinary 

 transposition of the bones that form its boundaries gives it a unique 

 character. Apparently the origin of this vacuity is the closing-in 

 of the bones surrounding pear-shaped orbits, as in Dimorphodon, 

 leaving an opening below the eyes ; but the form of the bones and 

 their positions are quite different. In the latter the jugal is 

 V-shaped, forming the anterior and lower boundaries ; and the 

 quadratojugal is triangular, comprising a moiety of the posterior 

 border, and uniting with the supra-temporal arcade, both bones 

 being vertical. 



