52 THE OLD RED SANDSTONE. 
** Do not be deterred,” said Agassiz, in the course of one of 
the interviews in which he obligingly indulged the writer of 
these chapters, who had mentioned to him that one of his 
opinions, just confirmed by the naturalist, had seemed so 
extraordinary that he had been almost afraid to communicate 
it, — ‘* Do not be deterred, if you have examined minutely, 
by any dread of being deemed extravagant. The possibili- 
ties of existence run so deeply into the extravagant, that there 
is scarcely any conception too extraordinary for nature to real- 
ize.” In all the more complete specimens which I have yet 
seen, the position of the jaws is vertical, not horizontal ; and 
- yet the creature, as shown by the tail, belonged unquestion- 
ably to the vertebrata. Now, though the mouths of the crusta- 
ceous animals, such as the crab and lobster, open vertically, 
and a similar arrangement obtains among the insect tribes, it 
has been remarked by naturalists, as an invariable condition 
of that higher order of animals distinguished by vertebral 
columns, that their mouths open horizontally. What I would 
remark as very extraordinary in the Coccosteus — not, how- 
ever, in the way of directly asserting the fact, but merely by 
way of soliciting inquiry regarding it —is, that it seems to 
unite to a vertebral column a vertical mouth, thus forming a 
connecting link between two orders of existences, by con- 
joining what is at once their most characteristic and most dis- 
similar traits.* 
* These statements regarding the character of the teeth and the 
position of the jaws of the Coccasteus have been challenged by very high 
authorities. I retain them, however, in this edition in their original 
form, as first made nearly six years ago. In atleast two of my speci- 
mens of Coccosteus the teeth and jaw form unequivocally but one bone — 
a result, it is not improbable, of some after anchylosing process, but 
