COMPARED WITH SCOTTISH TYPES — MICROSCOPICAL CHARACTERS. 67 
Scottish genus, the Coccosteus, yet been found in Russia ; for although, when upon 
the spot, we were disposed to consider certain mammillated scales and bones as 
belonging to that genus (see Proceedings of Geol. Society, vol. iii. p. 401), we now 
learn from the great ichthyologist, that it is not present, though its place is taken 
by the allied genera Glyptosteus and Chelonichthys. And here it is gratifying to 
reflect, that some of the more perfect specimens which we brought from Russia 
have enabled M. Agassiz to describe, for the first time, the less well-preserved frag- 
ments of bone which he formerly procured from Scotland, but which he had put 
aside as doubtful forms. All these Ganoid types, as well as the very peculiai 
Russian genus Pl.acosteus, Ag., and other Placoid fishes of the genera Ctenoptychius 
and Ctenacanthus, will be described in their appropriate place, accompanied by some 
ingenious observations of the author, on the analogies which a comparison ol the 
contents of the Russian and Scottish deposits has enabled him to draw, between the 
conditions of that ancient epoch, and the existing distribution of fishes in the dif- 
ferent seas of Europe (see Part III.). 
We cannot, however, quit this subject, without alluding to the great light which 
is thrown upon ancient nature, by the application of the microscope to fossil teeth 
and bones. To Professor Owen geologists are most indebted for the new employ- 
ment of this valuable power. First testing its importance in distinguishing Mam- 
malia and Saurians, he also applied it to certain teeth of fishes brought to him 
from Scotland, and discovering in them a dendridic disposition of the vascular 
canals, he named the genus Dendrodus. Now, on submitting to Professor Owen 
some teeth of similar outline and appearance from Riga in Russia, he detected b\ 
the same process, that they were absolutely identical with those from Scotland, 
which he had named Dendrodus strigatus as the type, with D. hastatus, D. bipor- 
catus and D. incurvus as subordinate species. In the subsequent account of the 
organic remains, this point will be illustrated by Professor Owen himself. 
But the value of this application of the microscope does not stop here, for whilst 
we write, Professor Agassiz acquaints us, that, availing himself ol the weapons 
which Professor Owen had so skilfully wielded, he has commenced a series of re- 
searches, not only into the teeth, but also into the structure of all the hard, enamelled 
bones of the Russian fossil fishes, and by which he will be able to show the same 
distinction in the other bones of the different genera of this class, which Professor 
Owen has successfully established in relation to the bones of the higher oiders of 
animals. He has, indeed, already forwarded to us a diagram which shows in three 
