SCALES AND DERMAL TEETH OF SOME GANOID AND PLACOID FISH. 461 
examining a portion of the opercular scale of this fish, I found it to be studded over 
with tubercles, fig. 25 a, like those in a piece of shagreen. On grinding away the 
under surface, so as to render the upper part transparent, there appeared beneath 
each tubercle a large lenticular cavity, fig. 25 &, which, as we shall subsequently show, 
is homologous with the pulp-cavity of the dermal teeth of placoid fish. From each 
cavity is given off a number of small tubular canals, fig. 25 c, which radiate outwards 
and upwards, and communicate with the external surface of the scale. The posterior 
portion of each tubercle, 25 d, is more prominent than its opposite extremity, evincing 
a disposition to become pointed and grooved on its surface. The tissue surrounding 
the bases of these tubercles is studded with numerous lacunae and a few scattered 
points, 25 e, constituting the orifices of canals which come up from below. On making 
a vertical section of the specimen, fig. 26, I found that the tubercle surmounting each 
cavity, fig. 26 a, was composed of kosmine with exceedingly fine branched tubes, 26 b, 
radiating from the cavity, 26 c, and covered over with and merging in a layer of 
transparent ganoin, 2Qd, which on its posterior margin exhibited the irregular super- 
ficial grooves already noticed. The kosmine consisted of a number of very dense but 
still distinct lamellae, arranged in concentric lines, which, superiorly, followed the 
curved outline of the tooth, and inferiorly, that of the roof of the subjacent cavity. 
Beneath each tubercle is this lenticular pulp-cavity, figs. 25 h, 26 h, the radiating pro- 
longations of which, 25 c, 26 e, proceeding upwards and outwards, form channels of 
communication with the external surface, reminding us of those existing in connec- 
tion with similar tubercles on the scale oi Dapidius granulosus. 
The textures which give support to these tooth-like appendages, consist of a series 
of osseous laminae, fig. 26 f, which are again subdivided into numerous minute lamellae. 
Amongst the inferior laminae are a number of very large cavities, which run into each 
other by means of narrow connecting passages, forming the homologues of Haversian 
canals, fig. 26 g. They send up narrow vertical branches to the external surface, 
which generally open at the small apertures, 25 e, but occasionally unite with one of 
the canals radiating from the lenticular pulp-cavities, fig. 26 A. 
The lowermost osseous laminae are not so thick, individually, as the upper ones, 
but they are more regularly uniform in size, as well as more parallel with the inferior 
surface, and with one another. 
Between the lamellae is a copious distribution of lacunae, many of the canaliculi of 
which radiate vertically as well as horizontally, perforating the lamellae, and thus 
establishing a communication between contiguous layers of lacunae. 
The specimens which I have had the opportunity of examining exhibited no trace 
of upturned lamellae in any part of their course, though their inflexions appear to 
have formed the large Haversian cavities, fig. 26 g. It is possible, however, that 
they may do so at tlie margin of the operculum, a portion which I have had no oppor- 
tunity of investigating, and which requires further attention. 
In addition to the canaliculi of the lacunae, we also find a considerable supply of 
MDCCCXLIX. 3 o 
