268 DENNIS, ON FOSSIL LIAS. 



cunae generally are then presented with their short axis in 

 view. The mammal that shows most irregularity in its lacunae, 

 as far as I have observed, is the walrus, and perhaps the 

 dugong. The definitions given appertain only to those 

 lacunae that appear in the haversian interspaces. Those that 

 form part of an haversian system have uniform and nearly 

 straight canaliculi proceeding from them, which in the 

 mammal generally are more numerous and finer, and less xoavy 

 than in the Saurian. 



The lacuna, fig. 4, is most remarkable for the great number 

 of canaliculi proceeding from it ; and from a photograph that 

 1 have of it,* they appear so numerous, that they are not dis- 

 tinguishable one from the other. Figs. 2, 2 a, beautifully exhibit 

 some of the lacunae in the fossil connected with an haversian 

 system, and very clearly show their mammal character.* They 

 bear a close comparison with the walrus ; and since that com- 

 parison is made with the recent bone of a mammal, it is easy 

 for any person who knows something about the microscopic 

 structure of bone, to form an opinion as to whether I am right 

 or wrong. For my own part, I cannot entertain a doubt upon 

 the question as to the bone belonging to some lower mammal. 

 But, at any rate, a new field is opened for the microscope ; 

 for the question I have raised must have a fair and scientific 

 solution. For if we are not able to discover the bones of 

 mammals and birds (and why we should not discover them I 

 know not, especially as the footmarks of the latter have been 

 already noticed), we shall at least be able to add new genera 

 and species to our existing list of reptiles and fishes. 



The Bristol bone-bed is a mine of animal matter. Let only 

 the microscope, with its splendid powers, be scientifically 

 used, and it must bring to light new treasures for science. In 

 investigating these matters, one thing ought ever to be borne 

 in mind, and which I have already adverted to — the connec- 

 tion or relation that the bone bears to the animal to which it 

 belongs. If this is not considered, I think our inquiry is 

 almost useless. We want not only to say that such a frag- 

 ment of bone belongs to a mammal or a fish, but we also 

 desire to be able to discover something of the general cha- 

 racter of the animal to which it belonged. 



In forming our judgment, then, concerning this or any 

 other fossil bone by its microscopic structure, we must do 

 pretty much what an anatomist would do under similar cir- 



* I had intended that fig, 2 a and fig, H should have been magnified the 

 same number of diameters ; the correspondence then would have been 

 more striking : but the reader must bear in mind that fig. 2 a is magnified 

 twice as many times as fig. 8, 



