SCALES AND DERMAL TEETH OF SOME GANOID AND PLACOID FISH. 447 
some of its details from that of P. comptus, the two evidently belong to one common 
type, which is distinct from any previously described. So far as the nutrition of the 
kosmine is concerned, the horizontal canals evidently fulfill the functions of the parallel 
vertical ones amongst the Lepidoti ; they do not appear to contribute any branches 
to the osseous lamellae, which, as in the case of the P. comptus, must be nourished 
through the lepidine tubes. 
Gyrodus. — The scale of a species of Gyrodus from Kellheim exhibited the appear- 
ance represented in fig. 9*. It is a modified form of the type found in the Lepi- 
dosteus, presenting similar laminae, lamellae, parallel tubes, and lepidine. The anterior 
portion of the scale, 9* a, which is very much thickened, exhibits well-marked con- 
centric lamellae, which become curiously inflected towards the centre of the scale. 
Owing to these inflections, the posterior portion, which rests on the thickened ex- 
tremity of the one behind it, suddenly becomes very thin, fig. 9* b, but still preserving 
its laminated structure, and divisible into two parts ; a lower one, in which the large 
tubes ascend from below, fig. 9* c, and an upper one, in which they enter from above, 
fig. 9* d. These tubes are much less numerous and less regularly arranged than in 
the majority of the preceding scales ; those especially which come from above exhi- 
biting less parallelism. The anterior extremity of the section, which when in situ has 
been deeply imbedded in the soft integument, is abundantly supplied with lepidine 
tubes, fig. 9=^e; those from the upper surface inclining downwards, and those from 
the lower margin running upwards in the direction of the centre of the scale. 
The sudden inflection of the laminae produces the appearance of the thick trans- 
verse rib, extending over the breadth, which is the longer axis, of the scale. 
Aspidorhynclius . — In the large scale of Aspidorhynchus acutirostris, from the litho- 
graphic stone of Solenhofen, we find a somewhat analogous structure to the last, 
only without the contracted inflections of the laminae. The bulk of the scale con- 
sists of an arrangement of lamellae, perforated by beautifully defined and regular 
parallel tubes, the interlamellar spaces being occupied by layers of magnificently 
developed lacunae with their branching canaliculi. These last are more beautiful 
than in any species of fish which I have examined. The upper surface of the scale 
exhibits a series of large and nearly parallel ridges and furrows : a vertical section 
(fig. 10 a) shows these ridges to be formed by an undulatory arrangement of the up- 
turned lamellae, which here take the place occupied by tbe ganoin amongst the 
Lepidoti. These undulating lamellae are perforated from above by a series of tubes, 
fig. 10 6, which, like those coming from below, fig. 10 c, terminate in a kind of neu- 
tral line between the upper and lower portions, which is about one-third of the thick- 
ness of the scale below its upper surface. 
If there is any ganoin upon the scale, it is so thin as to be invisible. Its place is 
occupied by these wavy lamellae ; and not only do the latter occupy its position, but 
they produce those superficial irregularities, which in Lepidosteus are due to the 
distribution of the ganoin : they have obviously been produced by the superior por- 
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