150 THE PLACOID -BRAIN. 



of Linnaeus belong, — liave the mouth not under, bus at the 

 anterior termination of the head, — in itself an esddence that 

 the position of the mouth at the extremity of the muzzle, 

 common to the greater number of the osseous fishes, can be 

 no very high character, seeing that the humblest of the Suc- 

 torii possess it ; and that many osseous fishes, whose mouths 

 open, not on the under, but the upper side of the snout, as 

 in th^ distorted and asymetrical genus Plaiessa, are not only 

 in no degree superior to their bony neighbours, and far infe 

 rior tc) the placoid ones, but bear, in direct consequence of the 

 arrangement, an expression of unmistakeable stupidity. [The 

 objection, however, admits of a greatly more conclusive reply. 

 " This fish, to speak in the technical language of Agassiz," 

 says the Edinburgh Keviewer, in reference to the ancient ich- 

 thyolite of the Wenlock Shale, " undoubtedly belongs to the 

 Cestraciont family of the placoid order, — proving to demon- 

 stration that the oldest known fossil fish [1845] belongs to 

 the highest type of that division of the vertebrata." I may 

 add, that the character and family of this ancient specimen 

 was determined by our highest British authority in fossil ich- 

 thology. Sir Philip Egerton.] And it is in depreciation of 

 Professor Sedgwick's statement regarding its high standing 

 that the author of the " Yestiges" refers to the supposed in 

 feriority indicated by a mouth opening, not at the extremity 

 of the muzzle, but under the head. Let us, then, fully grant, 

 for the argument's sake, that the occurrence of the mouth iu 

 the muzzle is a sign of superiority, and its occurrence under 

 the head a mark of inferiority, and then ascertain how the 

 fact stands with regard to the Cestracion. " The Cestracion 

 subgenus," says Mr James Wilson, in his admirable trea 

 tise on fishes, which forms the article Ichthyology in the 

 " Encyclopaedia Britannica," " has the temporal aperture, 

 the anal fin, and rounded teeth, of Squalus Mustelus ; hut 

 the mouth is terminal, or at the extremity of the pointed 



