in the Neighbourhood of Edinburgh. 207 



appeared no other resource left to this indefatigable naturalist, 

 than to inquire whether, in other examples of recent or fossil fish 

 allied to the Megalichthys, the larger or smaller teeth prevailed 

 most in number. If the larger or canine teeth should prove 

 to be fewer in number, and should have a more interior and 

 anterior position among the bones of the mouth, he conceived 

 that a great argument would be afforded for assimilating the spe- 

 cimen of Burdiehouse to that of Leeds, whence their identity 

 as one genus of fish, if not exactly established, would at least be 

 a reasonable presumption. 



Such a comparison was accordingly instituted, by which M. 

 Agassiz came to the conclusion, that in the lesser number of 

 larger or canine teeth, or, in other words, in the far greater pro- 

 portion of smaller teeth, the sauroid genus of Burdiehouse would 

 be ultimately found to identify itself with that of Leeds, and 

 that thus each animal would be referable to the Megalichthys. 



This anticipation has been remarkably confirmed in the sub- 

 sequent discovery of part of a jaw, too late for M. Agassiz to see 

 before he left England. It shews a larger tooth alternating with 

 several of much smaller size. The relic (See Plate X. fig. 1) evi- 

 dently belonged to a young animal, as it exhibits none of the im- 

 mense and similarly striated teeth which have been found in a 

 detached state. It, however, not only displays a larger tooth alter- 

 nating with an excess of smaller ones, but likewise a difference 

 of size between the two kinds, — so extraordinary, indeed, as to 

 afford an illustration of the advantages which were to be derived 

 from a comparison of isolated remains, with the connected ones 

 of other animals, at least approaching to one common family. 



But I shall now advert to other investigations of comparison. 



In the recent and very remarkable sauroid fish conceived to 

 be a living type of the Megalichthys, — the Lepidosteus spatula, — 

 M. Agassiz observed phenomena nearly similar. He states that 

 teeth of an inch long, alternate with small teeth which are not a 

 line in length. In this species, he adds, the largest teeth are 



