found in the Old Red Sandstone. 283 



and other respects to the recent scales of the Lepisosteus ana- 

 lysed by Chevreul. In regard to the Burdiehouse scales, this 

 was hardly a matter of any doubt, because the animal matter 

 was indubitably represented by a fine siliceous skeleton, and 

 the relative proportions of the three constituents, phosphate of 

 lime, carbonate of lime, and animal matter, plainly approached 

 very nearly in the recent and fossil scales. But, in the present 

 instance, the ratio of the phosphate to the carbonate of lime, is 

 quite different, being nearly as 13 to 1, instead of as formerly 

 about 4 to 1. Now, it is singular that two of the three analyses 

 of recent fish-scales which Chevreul has given us, present nearly 

 this ratio of 13 to 1. His analyses are, 



Perca labrax. 



Phosphate of Lime, . . . 37.80 



Carbonate of Lime, . . . 3.06 



Gelatinous Animal Matter, . . 55. 

 Phosphate of Magnesia, . . .90 



Fatty matter, .... .40 



Carbonate of Soda, ... .90 



98.06 100 



Now, all recent fish-scales which have been examined, contain a 

 large proportion of perishable animal matter, usually about half 

 their weight ; and in the case of the Burdiehouse fossil scales, 

 there is plain evidence, from the substituted siliceous matter, of 

 an original constitution similar in this respect. Let us suppose 

 that those at present under examination had originally con- 

 tained, like those of the Perch and Chaetodon, with which they 

 agree in the relative proportions of phosphate and carbonate, a 

 little more than half their weight of animal matter, which has 

 disappeared without substitution. On this view, their original 

 composition would have been nearly as follows, retaining the 

 present proportions between phosphate and carbonate : - 



Phosphate of Lime, . . . . 41.6 

 Carbonate of Lime, .... 3.2 

 Animal Matter, .... 55.2 



Phosphate of Magnesia and Chlorides, small 

 quantities. 



100 



This constitution would therefore have been entirely analogous 

 to that of the scales of the two recent fishes referred to. 



