24 
vol. vi. pl. 39, was a most improbable one to have sustained a power- 
ful wing of any bird!* Let me not be supposed, however, to be 
concerned in excusing my own mistake; I am only reducing the 
unamiable exaggeration of it. Above all things, in our attempt to 
gain a prospect of an unknown world by the difficult ascent of the 
fragmentary ruins of a former temple of life, we ought to note the 
successful efforts, as well as the occasional deviations from the right 
track, with an equal glance, and record them with a strict regard to 
truth. The existence of a species of Albatros, or of any other actual 
genus of bird during the period of the Middle Chalk, would be truly 
a wonder of Geology ; not so the existence of a bird of the longipen- 
nate family. 
I still think it for the interest of science, in the present limited 
extent of induction from microscopic observation, to offer a warning 
against a too hasty and implicit confidence in the forms and propor- 
tions of the Purkingean or radiated corpuscles of bone, as demon- 
strative of such minor groups of a class as that of the genus Ptero- 
dactylus. Such a statement as that “these cells in Birds have a 
breadth in proportion to their length of from one to four or five ; 
while in Reptiles the length exceeds the breadth ten or twelve times,”’ 
only betrays the limited experience of the assertor. In the dermal 
plates of the Tortoise, e. g., the average breadth of the bone-cell to 
its length is as one to six, and single ones might be selected of greater 
breadth. 
With the exception of one restricted family of Ruminants, every 
Mammal, the blood-dises of which have been submitted to examina- 
tion, has been found to possess those particles of a circular form: in 
the Camelide they are elliptical, as in birds and reptiles. The bone- 
cells have already shown a greater range of variety in the Vertebrate 
series than the blood-dises. Is it then a too scrupulous reticence to 
require the evidence of microscopic structure of a bone to be corrobo- 
rated by other testimony of a plainer kind, before hastening to an 
absolute determination of its nature, as has been done with regard to 
the Wealden bone, figured in the Geol. Trans., 2nd Series, vol. v. 
pl. 13. fig. 6+? As a matter of fact, the existence of Pterodactylian 
remains in the chalk was not surmised through any observation of the 
microscopic structure of bones that are liable to be mistaken for those 
of birds, but was first plainly proved by the characteristic portions of 
the Pterodactyle defined by Mr. Bowerbank, as follows, in his original 
communication of this discovery to the Geological Society of London, 
May 14, 1845 :-— 
“T have recently obtained from the Upper Chalk ¢ of Kent some 
* Mantell, ‘ Wonders,’ &c. ed. 1848, vol. i. p. 441. 
t+ Compare, for example, two of the longest of the cells figured by Mr. Bower- 
bank in pl. 1. fig. 9, ‘Quarterly Journal of the Geological Society,’ vol. iv. as those of 
a bird, with two of the widest of the cells figured in fig. 1 of the same plate as those 
of the Pterodactyle; and contrast the want of parallelism in the bone-cells of the 
Wealden bone, fig. 9, with the parallelism of the long axes of the cells in that of 
the Albatros, fig. 3. 
+ Mr. Toulmin Smith, in an able paper ‘‘ On the Formation of the Flints of the 
