SCALES AND DERMAL TEETH OF SOME GANOID AND PLACOID FISH. 463 
low as well as above it. Similar canals communicate between the pulp-cavity and the 
upper surface, fig.- 27 d. Beneath this superficial tissue we find another structure, 
composed of numerous thin parallel lamellae, which gradually ascend as they proceed 
from the anterior towards the posterior margin of the scale, fig. 27 e; and upon the 
outcropping edges of which, to employ a geological illustration, the more superficial 
layer rests in unconformed stratification. No true lacunae appear to enter into the 
structure of these lamellae, but between them are layers of small irregular tubes, 
which anastomose freely with one another ; those found on opposite sides of each 
lamella, like the fusiform lacunae of IMegalichthys, usually running in different 
directions, so as to give to the horizontal section the aspect of network. These do 
not appear to be modified lacunae, but seem more analogous to lepidine tubes. 
They give off numerous branches, which pass through the lamellae, keeping up a 
communication between contiguous layers. 
Fig. 28 is a section of one of the rows of large teeth from the centre of the scale. 
In this specimen, from which the lower laminae have been accidentally detached, as 
is usually the case, the tubercles are developed into the form of regular pointed 
dermal teeth, each having a pulp-cavity, fig. 28 a, from which spring small branching 
tubes, 28 b, like those seen in the dermal teeth of ordinary Placoids. Each one ex- 
hibits a laminated structure like that seen in the true teeth of reptiles, the lamellae 
being arranged as a succession of cones, having evidently been formed by the addi- 
tion of new internal layers organized around the soft pulp. In fact, it is only one 
of the laminated tubercles of the operculum, fig. 26 a, drawn out vertically; the len- 
ticular space, fig. 26 c, being also elongated in the form of a true pulp-cavity, whilst, 
in consequence of this modification of the external contour, the lamellae have assumed 
the appearance of a succession of cones inclosing each other. At the base of each 
tooth we still find the radiating canals, fig. 28 J, communicating with the exterior of 
the scale, as in those of the operculum. 
Fig. 28 e represents the externally grooved appearance of each tooth, the section 
not having passed completely through its centre. 
The most extraordinary feature in the anatomy of this singular fish yet remains to 
be described. In its interior there is invariably found a long hollow fusiform viscus, 
which has generally been regarded as a stomach. M. Agassiz, who entertained this 
opinion, says, “II ressemble a un cylindre squammeux, et cet aspect est evidemment 
le resultat des changemens survenus dans les ditferentes membranes qui en com- 
posaient les parois.” 
On mounting prepared sections of this “membrane,” I found that it consisted of 
true laminated bony tissue. When a vertical section was made through its entire 
thickness parallel to the long axis of the viscus, it presented the appearance repre- 
sented in fig. 30. It chiefly consists of horizontal lamellse, fig. 30 a, between which 
are developed large lacunae, fig. 30 h, identical with those found in the bones of its 
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