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 
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 P¢. 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 Pé. Cuvieri, and are more numerous than in the P¢. gigan- 
teus ; they are probably also more numerous than in the Pt. Cuvieri 5 
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 (Pl. IT. figs. 1, 2, 3), that the jaw of the P¢. com- 
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 striz of the outer surface are more continuous 
than in the Pt. Cuvier, 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 Pé. compressirostris. This species belongs, more de- 
cidedly than the Pé. 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 Pé. 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 from 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. Bowerbank’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.—Procerpines or THE ZOOLOGICAL Sociery. 
