Zoological Society. 



versely. It is perforated by a few small irregular vascular foramina. 

 There are no orifices on the inner side of the alveoli ; the successioual 

 teeth emerge, as in the Crocodiles, from the old sockets, and not, as 

 in certain Mammalia and Fishes, by foramina distinct from them. 

 The second and third alveoli are the largest ; the fourth, fifth and 

 sixth the smallest, yet they are more than half the size of the fore- 

 going, with which the rest are nearly equal. The outlets of the alveoli 

 are elliptical, and they form prominences at the side of the jaw, or 

 rather the jaw sinks gently in between the alveoli, and is continued 

 into the bony palate without any ridge, the vertical wall bending round 

 to form the horizontal plate. The greatest breadth of the under sur- 

 face of the jaw, taken from the outside of the alveoli, varies only from 

 seven lines across the third pair to nine lines across the eleventh pair 

 of alveoli ; and from the narrow base the sides of the jaw converge 

 with a slight convexity outwards at the anterior half of the fragment, 

 but are almost plane at the deeper posterior half, where they seem to 

 have met at one acute superior ridge ; indeed such a ridge is con- 

 tinued to within an inch of the fore part of the jaw, where the upper 

 border becomes more obtuse. 



The whole portion of the jaw appears to consist of one uninter- 

 rupted bone — the premaxillary ; the delicate crust of osseous sub- 

 stance, as thin as paper, is traversed by many irregular cracks and 

 fissures, but there is no recognizable suture marking off the limits of 

 a maxillary or nasal bone. The bone offers to the naked eye a fine 

 fibrous structure, so fine as to produce almost a silken aspect, the 

 fibres or striae being longitudinal, and impressed at intervals of from 

 two to six lines by small vascular foramina. 



Having premised so much with reference to the characters of the 

 Pt. Cuvieri, I proceed to the description of the distinct species, for 

 which I propose the name of Pterodactylus eompressirostris. 



Pterodactylus compressirostris, Owen. 



This species is represented by two portions of the upper jaw, 

 obtained from the Middle Chalk of Kent, the hinder and larger 

 of which include the beginning of the external nostril. The depth 

 of the jaw at this part is fourteen lines, whence it gradually de- 

 creases to a depth of ten lines at a distance of three inches in advance 

 of this, indicating a jaw as long and slender as in the Pt. longirostris, 

 supposing the same degree of convergence of the straight outlines of 

 the upper and alveolar borders of the jaw to have been preserved to 

 its anterior end : that this was actually the case is rendered most 

 probable by the proportions of the smaller anterior part of the jaw 

 obtained from the same pit, if not from the same block of chalk, 

 and which, with a vertical depth of seven lines at its hinder part, 

 decreases to one of six lines in an extent of one inch and a half in 

 advance of that ])art. The sides of the jaw as they rise from the 

 alveolar border incline a little outwards before they converge to meet 

 at the upper border. This gives a very narrow ovoid section at 

 the fore part of the larger fragment, the greatest diameter at its 

 lower half being four lines, ancl^tlie sides meeting above at a slightly 

 obtuse ridge. This vn y gradually widens as the jaw recedes back- 



