Ba ease es MO. SOLE ried, Wer 
2 Prof. Owen on the Structure of the Teeth of some Fossil Fish. 41 
in bundles. At first the frond contains only one or two fila- 
ments (as correctly stated by Mr. Hassall in his ‘ British Fresh- 
water Aleve’); but these dividing as in Oscillatoria, the inflated 
frond becomes completely filled and at length ruptured, when 
the filaments escape from it to form new plants. 
I intend in a future communication to offer some evidence in 
proof that the appositional branches in Rivularia, Calothriz and 
other genera are merely modifications of the mode of growth here 
described. 
VII.—On the Structure of the Teeth of some Fossil Fish of the 
Carboniferous Period. By Prof. Own, F.R.S. 
To the Editors of the Annals of Natural History. 
GENTLEMEN, 
In the interesting and instructive summary of the modifications 
of the teeth im fossil fishes of the carboniferous period which 
Mr. M‘Coy has given in the ‘Proceedings of the Cambridge 
Philosophical Society,’ June 1848, he notices a layer of true 
enamel in ‘ Centrodus, which he says “is quite distinct from 
that dense modification of dentine, which, forming the polished 
surface of most fish-teeth, has been confounded with true enamel, 
but which it is here proposed to call ‘ ganoine’ in future descrip- 
tions” (p.65). I have long been inthe habit of applying the 
term ‘ ganoine’ to the peculiar tissue which forms the enamel- 
like surface of ‘ ganoid scales ;? but, as the term has been pub- 
lished by me in no other way than orally in lectures, I should be 
willing to resign it for the new dental tissue which Mr. M‘Coy 
professes to have discovered, if his claim to the discovery were 
sound. If I mistake not, Mr. M‘Coy first announced his discovery 
in your ‘August Number’ of the present year, p. 124, where, 
after animadverting on the frequent mistake of his new modifi- 
cation of dentine for true enamel, he says : ‘‘ The latter is, how- 
ever, secreted by a distinct organ quite external to and indepen- 
dent of the dentine, while the false enamel, which I propose to 
eall ‘ ganoine,’ is merely produced by the calcigerous tubes of the 
‘dentine becoming suddenly straighter, closer and more numerous 
as they approach the surface ” (p. 124). 
In my ‘Odontography’ I defined what I believe to be the 
“ganoine’ of Mr. M‘Coy in the following words: “In some in- 
stances, as in the teeth of the flying-fish (Hzocetus) and sucking- 
fish (Remora), the substance of the tooth is uniform, and not 
covered by a layer of a denser texture. In others, as the shark, 
sphyreena, &c., the tooth is coated with a dense, shining, enamel- 
