DENNIS, ON FOSSIL BONE. 63 



made, and is destined still further to create, great changes in 

 our knowledge of the structure and classification of the more 

 minute lichens. It has been lately determined that the 

 genus Pyrenothea constitutes the spermogonesof various more 

 familiar lichens,— e. g., P. leucocephala, Fr., consists of the 

 spermogones of Lecidea abietina, Ach., and P. vermicelli/era, 

 Kunz, of those of Biatora hdeola, Fi*. 



"Pycnodites nondum innotuimnt," remarks Tulasne tersely. 

 This statement my own experience — as I have already men- 

 tioned in describing the pycnides of ^. Sniithii — enables me 

 to corroborate. 



The existence of Birds during the deposition of the Stones- 

 field Slate proi'ed by a compariso7i of the Microscopic 

 Structure of certain Bones of that formation ivith that 

 o/ Recent Bones. By the Rev. J, B. P. Dennis^ F.G.S., 

 Bury St. Edmunds. 



From extensive observations made upon the bones of birds, 

 1 find that, in their microscopic characters, their bones are 

 as distinct from those of mammifers as the latter are from 

 the bones of sanrians. As the lacuna in the saurian bone 

 exceeds that of the mammal in the size of its canalicidi, so 

 does the latter exceed that of the bird ;"^ and as they are more 

 numerous and more branched in the bird than in the 

 mammal, so in like manner are they more so in mammalian 

 than in saurian bone. 



It is in birds that the Haversian tubes attain their most 

 elegant and varied reticulations, not fortuitously, but with 

 design, and that intimately connected with the life and 

 habits of the animal. In fact, each bone is a study in itself, 

 and involves a knowledge of the muscles that move it as well 

 as of the use it is designed for ; and in a bird of flight the 

 shape of the wing, the extent of the surface covered by the 

 quill feathers, whether it is pointed or round, whether the 

 secondary quills are strong or w^eak, are all matters of deep 

 consideration, and comparison with the internal structure of 

 the bone, Avhich the microscope reveals to the eye. I feel 

 that I need the povrers of the coiLsummate naturalist and 



* Tills, of course, is speaking generally. I do not observe much differ- 

 ence between the caiialiculi of the hare and those of Bewick's swan as to 

 size. Again, the lacuna of the mole are as small as those of birds, but 

 then the Haversian tubes totally differ. As a general rule, the bone-cell^ 

 in birds arc smaller than they are in mammifers. 



