890 Zoological €ociety. 



wards, where the eiitireness of the walls of the smoothly convex upper 

 part of the jaw proves that the narrowness of that part is not due to 

 accidental crushing. Had that been the case, the thin parietes arch- 

 ing above from one side to the other would have been cracked. The 

 only evidence of the compression to which the deep sides of the jaw 

 have been subject is seen in the bending hi of the wall above the 

 filveoli, close to the upper ridge at the fore part of the fragment. 



In an extent of alveolar border of three and a half inches there are 

 eleven sockets, the anterior one on the right side retaining the fraC" 

 tured base of a tooth : the alveoli are separated by intervals of about 

 one and a half times their own diameter ; their outlets are elliptical, 

 and indicate the compressed form of the teeth : they are about two 

 lines in long diameter at the fore part of this fragment, but diminish 

 as they are placed more backwards, the last two being developed be- 

 neath the external nostril. The bony palate is extremely narrow, 

 and presents in the larger portion a median smooth convex rising 

 between two longitudinal channels, which are bounded externally by 

 the inner wall of the alveolar border. There is no trace of a median 

 suture in the longitudinal convexity. The breadth of the palate at the 

 back part of the fragment is eight lines ; at the fore part it has gra- 

 dually contracted to less than three lines, but it is somewhat crushed 

 here. The naso-palatine aperture commences about half a line in 

 advance of the external nostril, three inches behind the fore part 

 of the larger portion of the upper jaw ; which exemplifies the cha- 

 racteristic extent of the imperforate bony palate formed by the long 

 single premaxillary bone in the genus Ptcrodactylus. The frag- 

 ment from the m.ore advanced part of the jaw contains five pairs 

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

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

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

 cing 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. (/iga7i- 

 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 preserved, that the jaw of the Pt. compressirostris extended 

 seven inches in front of the nostiil, it could not have contained less 

 than twenty pairs of alveoli, according to the nvmiber and arrangement 

 pf those in the two portions preserved. 



The osseous walls in both portions present the characteristic com- 



