6 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 9, 
one of these bones, corresponding with fig. 1 a, Pl. II. of Mrs. Smith’s 
pair, measures 24 inches at its greatest diameter, while that of Mrs. 
Smith’s specimen is 14 inch only. The animal to which such bones 
belonged could therefore have scarcely measured less than fifteen or 
sixteen feet from tip to tip of its expanded wings. 
In the bone belonging to Mr. Toulmin Smith, represented by fig. 4. 
Pl. II., there is an orifice at a which has every appearance of being 
a pneumatic foramen. Iam not aware that such orifices have hitherto 
been observed in the bones of Pterodactyls, but I can see no good 
reason why they should not have been furnished with them. The 
whole structure of the skeleton, and the extreme thinness of the 
bones, proclaim them as eminently volant; and as we find among 
birds that those which are destined to be most continuously upon the 
wing are furnished to the greatest extent with pneumatic cavities in 
their bony skeleton, so we may reasonably expect that m a reptile so 
especially constructed for flight, nature would not fail m contributing 
organs so essential to the end_of their peculiar construction. 
The bone described and figured No. 2 by Prof. Owen was in a 
somewhat mutilated condition, but the head of Mr. Toulmin Smith’s 
specimen is in a remarkably fine state of preservation. From acom- 
parison of this specimen with the plate of Pterodactylus Macronyz, 
described by Dr. Buckland in the Geological Transactions, Feb. 6, 
1829, there is every appearance that it is the corresponding bone to 
that indicated by N', or the left femur of the animal. I have also 
compared it with the original in the British Museum, but unfor- 
tunately that valuable specimen has suffered so much dilapidation 
since the plate was engraved that the representation affords a much 
better reference than the original. 
The satisfactory nature of the results of the examinations which I 
have detailed, led me to believe that I should be rendering an ac- 
ceptable service to science if I were to extend my researches to other 
disputed bones beside those from the chalk. I therefore applied to 
Dr. Buckland for permission to examine in like manner the jaws from 
the Stonesfield slate, in the hope that their structural peculiarities 
would assist in deciding the long-mooted question of their mammalian 
or reptilian nature. To this request Dr. Buckland responded in the 
readiest and most liberal manner, by removing in my presence small 
portions of each of these rare and valuable specimens represented by 
figs. 1 and 3. Pl. 5. vel. vi. Transactions of the Geological Society, 
2nd Series. Upon immersing these minute fragments in Canada balsam 
and examining them by transmitted light with a power of 500 lmear, 
I found the bone-cells were to be seen in the most beautiful manner, 
and especially those from the jaw represented by fig. 3 im the Plate 
of the Transactions of the Geological Society. The small fragment 
removed had fortunately splintered off in the direction of the course 
of the fibres of the bone, so that the length and proportions of the 
cells were rendered in the most satisfactory manner, as represented 
by fig. 6. Pl. I. Upon accurately measuring five of these, their 
average gave the following dimensions : length 54,, greatest diameter 
azosz- The minute canaliculi were apparent in great abundance, 
