LOWER OLD RED SANDSTONE OF SCOTLAND. 335 



have one of tlie modern keys by which these ancient signs 

 are interpreted. It tells us that they are true ichthyodoru- 

 lites, but leaves us in doubt whether the larger spine, resem- 

 bling that of HoplacanthuSj belonged to a placoid or ganoid, 

 and gives us no positive information regarding the structure 

 of the creature to which they belonged : we can merely in- 

 fer that, perhaps in the degree in which the ancient spines 

 resemble those of recent times, the ancient ichthy elite that 

 bore them resembled the modern spine-bearing fish. The 

 ganoidal remains, on the other hand, we find charged with 

 positive, and often very minute information. In this speci- 

 men [Spec. 3], specially referred to by Agassiz in his great 

 work, and which I have derived from the fish-beds of Cro 

 mai-ty, there is the head and upper part of the body of a ga- 

 noid preserved, — ^the Osteolepis microlepidotus ; and it exists, 

 not as the mere sign of a fish, but as a considerable portion 

 of a fish, from the study of which interesting facts can be 

 absolutely determined. It will be seen from the following 

 passage what it is that Agassiz has positively determined from 

 this very fossil " In a specimen of the Osteolepis microle- 

 pidotuSj^ says the distinguished ichthyologist, " which is to 

 be seen in the collection of Mr Hugh Miller, three quarters 

 of the head are preserved ; and as the superior surface and 

 the sides are equally visible, I have succeeded in convin- 

 cing myself that the nostrils, which are situated before the 

 frontals, are separated in their whole length by a medial su- 

 ture, — a peculiarity which in our day is only to be met with 

 in the Lepidosteus of America." There are several of the 

 other fossils on the table that give equally conclusive evidence 

 of the sense of smell, as indicated by the nostrils. 



Let us inquire whether they can tell us aught regarding 

 the other senses by which the fishes of the Old Red Sandstone 

 took note of the material and external. We must, of course 

 restrict the inquiry to the four cerebral senses j for of the 



