60 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
two examples of symphysial dentition, we may pass on to their detailed 
description ; and as they fortunately supplement each other, and occu- 
pied without doubt the same position in the mouths of two precisely 
similar individuals, it will be more convenient to consider them to- 
gether instead of separately. In the first place, however, we must 
conceive of the dentition of Campodus having been developed as 
follows: as the newly formed successional teeth were pushed up from 
the supporting cartilage, they were carried forward in regular order, 
gradually increasing in size with the age of the individual, while 
the functional teeth which they replaced were not shed, but became 
rotated over on to the outer side of the jaws. Everywhere, except in 
front, the unrolling of these series proceeded in a more or less spiral 
fashion, after the manner of Cestracion. And as in this recent genus, 
also, the symphysial series were bilaterally symmetrical and coiled in a 
single plane. The number of symphysial teeth, and curvature of the 
series, is practically the same in both genera. 
It is interesting to note in this connection, that a relic of ancestral 
conditions still persists in Cestracion, in that occasionally the median 
azygous series of the lower jaw is somewhat enlarged, while opposed to 
it in the upper jaw, two corresponding series, one on either side, are also 
slightly enlarged. | Chlamydoselache and some other recent sharks pos- 
sess a median azygous series in the lower jaw, opposed to which is 
a paired series in the upper. The selfsame arrangement is very con- 
spicuous in Campodus, where the two examples before us obviously 
represent the unpaired median series, and, as shown by marks of wear, 
played against a corresponding paired series in the opposite jaw. 
These two corresponding series were, however, separated by an interval, 
so as to include the azygous series for a greater part of its width 
between them when the jaws were closed. So far as we may depend 
on analogy, the conclusion is warranted that the two specimens of 
symphysial dentition before us pertain to the lower jaw, and that 
examples of paired series belonging to the upper jaw have not as yet 
been encountered. 
Two facts deserve to be specially noted, for reasons which will at once 
present themselves. In the first place we observe that the symphysial 
dentition of Campodus is bilaterally symmetrical and curved or inrolled 
in a single plane. And, secondly, the symphysial teeth are very dis- 
proportionately enlarged with respect to the antero-lateral series, the 
disparity being in fact greater than is known to occur in any other 
genus, recent or fossil. 
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