Vol. 6 9. J SKELETON OP OBNITHODESMUS LATTDENS. 411 



The confluent nares and preorbital fossae of Pterodaetylus caused 

 by the degradation of the maxillo-nasal bar, and the reduction in 

 dimensions of all the apertures of the skull in Rhamphorhynchus, 

 show that their structure became modified in a direction opposite 

 to that followed by Omiiliodesmus. It is generally conceded that 

 the skull of the recent Sphenodon punctatus is near the primitive 

 type of the reptilian skull: tScaphognaikus, Dlmorphodon, and Orni- 

 thodesmus have retained its perforated character, Pterodaetylus less 

 so, and Rhamphorhynchus and Ornithostoma least. The .modifi- 

 cations proceeding in these skulls were radically at variance. In 

 Pterodaetylus the maxillo-nasal bar had almost, if not entirely 

 disappeared. It is said to exist in some examples of Pt. elegans 

 (syn. Pt. pulchellus, according to Zittel), which demonstrates what 

 hud degenerated in the other species. How much significance can be 

 attached to the small fragment of bone, hanging from the ventral 

 surface of the posterior end of the premaxillar extension over 

 the preorbital vacuities, cannot be decided. Hermann von "Meyer 

 thought it a prefrontal, which Dr. Plieninger 1 considers an attrac- 

 tive theory, but one that has yet to be proved. It may or may 

 not be the vestige of the arch, but certain it is that the bars have 

 disappeared or contracted. Ptenodracon brevirostris, a genus which 

 must be included within the sub-order Pterbdactyloidea, also retains 

 the maxillo-nasal bar. 



In Rhamphorhynchus the apertures were gradually closing in. 

 In Eh. Jongiceps 2 the skull retained more of the open character than 

 in any other species of this genus. The obliteration of the fossae 

 had proceeded farthest in the skulls of Ornithostoma and Nyctosaurus 

 (syn. NyctodactyJus). In the latter the antorbital fosssehad become 

 quite vestigial. 3 The tendency of most forms through time has 

 been to reduce the size of the teeth, and lose the posterior dentition. 

 In some species of Rliamphorhynchus the loss is" seen to be in the 

 reverse direction, commencing from the tip of the beak backwards. 

 In Ornithostoma and Nyctosaurus the edentulous jaws prove that 

 a final stage had been reached. Although there are only small 

 moieties of the jaws to reason upon, I consider that the genera of 

 the Cambridge Greensand belong to the Khamphorhynchidse. In 

 some the teeth were retained, but the beaks were growing more 

 attenuated and lance-like. In others the muzzle was retracting 

 axially, causing the tip to deepen vertically and thicken laterally. 

 The bold convexity of the dorsal outline and the depth of the 

 beaks may suggest origin from iScaphognathiis ; but the extremely- 

 light build of that skull could not have supported at its extremity 

 so heavy a weight as the obtuse ponderous tip, without buckling. 

 All these genera can be dismissed, as having no near affinity to 

 Omithodesmus. The latter is quite outside the genus Ornitho- 

 eheirus : for, according to Seeley's amended definition of the genus, 

 the characters are (i) teeth prolonged anterior to the muzzle, (ii) a 



1 ' Pterosaur, d. Jura Schwabens' Palajontographica, vol. lib (1907) p. 294.i, 



2 A. S. Woodward; Ann. Mag. Nat. Hist. ser. 7, vol. ix (1902) p. 4 & pi. 

 fig. 3. 



3 S. W. Williston, Journ. Geol. (Chicago) vol. x (1902) p. 526. 



