60 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



two examples of syraphysial 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 

 az3'gous 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 mai-ks 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 fticts 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 tlie antero-lateral series, the 

 disparity being in fact greater than is known to occur in any other 

 genus, recent or fossil. 



