33 



long single premaxillary bone in the genus Pterodactylus. The frag- 

 ment from the more advanced part of the jaw (fig. 3') contains five 

 pairs of alveoli in an extent of two inches, these alveoli being rather 

 lai'ger and closer together than in the hinder part of the jaw. Owing 

 to the compression which the present portion has undergone, the ori- 

 fices of the alveoli are turned outwards, the bony palate being pressed 

 down between the two rows, and showing, as the probable result of 

 this pressure, a median groove between two longitudinal convex ridges ; 

 but the bone is entire and imperforate. 



The form of the upper jaw in the present remarkable species differs 

 widely from that of the two previously known species from the chalk, 

 in its much greater elongation and its greater narrowness ; and from 

 the Ft. Cuvieri, in the straight course of the upper border of the jaw, 

 as it gradually converges towards the straight lower border in advanc- 

 ing to the anterior end of the jaw. The alveoli, and consequently the 

 teeth, are relatively smaller in proportion to the depth of the jaw than 

 in the Pt. Cuvieri, and are more numerous than in the Pt. ffiffan- 

 teus ; they are probably also more numerous than in the Pt. Cuvieri ; 

 although, as the whole extent of the jaw anterior to the nostril is not 

 yet known in that species, it would be premature to express a decided 

 opinion on that point. As we may reasonably calculate from the frag- 

 ments preserA^ed (PI. II. figs. 1, 2, 3), that the jaw of the Pi. coni- 

 pressirostris extended seven inches in front of the nostril, it could not 

 have contained less than twenty pairs of alveoli, according to the num- 

 ber and arrangement of those in the two portions preserved. 



The osseous walls in both portions present the characteristic com- 

 pactness and extreme thinness of the bones of the skull of the genus : 

 the fine longitudinal strise of the outer surface are more continuous 

 than in the Pt. Cuvieri, in which they seem to be produced by a suc- 

 cession of fine vascular orifices produced into grooves. The conspi- 

 cuous vascular orifices are almost all confined to the vicinity of the 

 alveoli in the Pt. compressirostris. This species belongs, more de- 

 cidedly than the Pt. Cuvieri, to the ' longirostral ' section of the Pte- 

 rosauria : whether it had an edentulous prolongation of the fore part 

 of the upper and lower jaw remains to be proved. 



In attempting to form a conception of the total length of the head 

 of the very remarkable species of Pterodactyle represented by the 

 portions of jaw above described, we should be more justified by their 

 form in adopting the proportions of that of the Pt. longirostris than 

 in the case of the Pt. Cuvieri : but allowing that the external nostril 

 may have been of somewhat less extent than in the Pt. longirostris, 

 we may still assign a length of frou^ fourteen to sixteen inches to the 

 skull of the Pterodactyle in question. 



It could not have been anticipated that the first three portions of 

 Pterodactylian skull — almost the only portions that have yet been 

 discovered in the cretaceous formations — should have presented such 

 well-marked distinctive characters, one from the other, as are de- 

 scribed and illustrated in Mr.Bowcrbank's Memoirs and in the present 

 communication. Such, nevertheless, are the facts : and, however im- 

 probable it may appear, on the doctrine of chances, to those not con- 

 No. CCXXI. — Proceedings of the Zoological Society. 



