382 Zoological Society. 



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- 

 dactyhis. 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-discs of which have been submitted to examina- 

 tion, has been found to possess those particles of a circular form : in 

 the Camelidce 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-discs. 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 Wcalden bone, figured in the Geol. Trans., 2nd Series, vol. v. 

 pi. 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 :— 



" I have recently obtained from the Upper Chalk f of Kent some 

 remains of a large species of Pterodactylus. The bones consist of — 



" 1 . The fore part of the head as far as about the middle of the 

 cavitas narium, with a corresponding portion of the under jaws, 

 many of the teeth remaining in their sockets. 



"2. A fragment of the bone of the same animal, apparently a part 

 of the coracoid. 



" 3. A portion of what appears to be one of the bones of the auri- 

 cular digit, from a chalk-pit at Hailing. 



*'4. A portion of a similar bone, from the same locality as No. 1. 



" 5. The head of a long bone, probably the tibia, belonging to the 

 same animal as the head. No. 1 . 



"6. A more perfect bone of the same description, not from the 

 same animal, but found at Hailing." 



* Compare, for example, two of the longest of the cells figured by Mr. Bower- 

 bank in pi. 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. 



t Mr. Toulmin Smith, in an able paper " On the Formation of the Flints of the 

 Upper Chalk," in the 'Annals of Natural History,' vol. xx. p. 295, affirms that no 

 upper chalk exists in the localities whence the above-defined specimens came. 

 They are from the " Middle Chalk." 



