THE PLACOID BRAIN. 151 



MUZZLE." The accompanying figure (fig. 55), taken from a 

 specimen of Cestracion in the collection of Professor John 



Fig. 65. 



PORT- JACKSON SHABK (Cestrodon Pkillippi). 



Fleming, may be recorded as of some little interest, both from 

 its direct bearing on the point in question, and from the cir- 

 cumstance that it represents, not inadequately for its size, the 

 sole surviving species (Cestracion Phillippi) of the oldest ver- 

 tebrate family of creation. With this family, so far as is yet 

 known, ichthyic existence first began.* It does not appear 

 that on the globe which we inhabit there was ever an ocean 

 tenanted by living creatures at all that had not its Cestracion, 

 — a statement which could not be made regarding any other 

 vertebrate family. In Agassiz's " Tabular View of the Ge- 

 nealogy of Fishes," the Cestracionts, and they only, sweep 

 across the entire geologic scale. And, as shown in the figure, 

 the mouth in this ancient family, instead of opening, as in the 

 ordinary sharks, under the middle of the head, to expose them 

 to the suspicion of being creatures of low and embryonic cha- 

 racter, opened in a broad, honest-looking muzzle, very much 

 resembling that of the hog. The mouths of the most ancient 

 placoids of which we know anything, did not, I reiterate, 

 open under their heads. 



* The reader now knows that with fishes akin to the Siluroids ichthyic 

 tsxistence began, or he may regard placoids and ganoids as contemporaries. 



