SCALES AND DERMAL TEETH OF SOME GANOID AND PLACOID FISH. 441 
analogous form of dentine. But what I more especially sought for I obtained, in the 
comparative ease with which vertical sections could be torn into fragments along the 
lines of the original lamellae, in the same way that Dr. Sharpey has demonstrated in 
the case of human bone*. This result left no doubt on my mind as to the applica- 
bility of the views of Leeuwenhoek and Agassiz to the scales of Lepidosteus osseus, 
being thoroughly convinced that their formation was accomplished by the successive 
organization of separate lamellae, though this organization was not confined, as 
imagined by Leeuwenhoek, to the inferior surface. 
I may observe, that on decalcification, the lacunae and tubuli did not disappear, as 
is stated by M. Agassiz, though they became somewhat less distinct, as they do in 
human bone under similar circumstances. This latter example has been already 
explained by Dr. Sharpey'I'; and his explanation is probably applicable to these bony 
scales : consequently the circumstance of the lacunae and tubuli becoming somewhat 
less conspicuous after decalcification, does not militate, against the idea of their being 
cavities. 
Did any doubt exist however on this point, the long streams of air-bubbles which 
issue out of them on mounting a section in Canada balsam would settle the question. 
Employing this scale of Lepidosteus as a valuable, and I believe the only recent, 
type of its class, we will proceed to examine those of some of the numerous fossil 
genera which have been constructed upon the same general plan. These are espe- 
cially the widely-diffused genera of Lepidntus, Seminotus, Dapidius, Tetragonolepis, 
Pholidotus and Ptycholepis. 
Lepidotus. — The scales of two species of this genus have already been examined by 
M. Agassiz with reference to their microscopic structure, L. unguiculatus and L.gigas. 
Of the former, he merely notices the superimposed arrangement of the lamellee;}:. Of 
the latter he says, “ Lorsque I’email est enleve, on aperqoit a la surface de la partie 
osseuse les bords des lames d’accroissement dont se composent les ecailles, et de 
distance en distance des lignes plus marquees, indiquant des interruptions dans I’ac- 
croissement ; elles sont causees par I’lisure des bords des dernieres lames qui ont 
precede un nouveau developpement. Je me suis assure par I’examen des poissons 
vivans que ces interruptions etaient periodiques et annuelles'^.” 
The most beautiful scale belonging to the genus which has come under my notice, 
is that of the L. semiserratus, from the Whitby lias, two representations of which are 
given in figs. 3 and 4. The general form of the scale is rhomboidal, having one of its 
free margins furnished with large teeth, two other sides of the rhomboid having been 
imbedded in the soft integument, and overlaid by the margins of the adjoining scales. 
On making a vertical section of the scale (fig. 3) in the direction of the lateral line, 
we find it to consist of well-marked parallel lamime, varying from - 2 ^th to ^^th of 
an inch in thickness, which, as in Lepidosteus, though in a less degree, are turned 
* Dr. Quain’s Anatomy, 5th edition, by Dr. Sharpey and Mr. Quain, p. cxlii. t Ut supra. 
J Poissons Fossiles, vol. ii. p. 253. § Ibid. vol. ii. part 1, p. 237. 
