OF THE EARLIER GANOIDS. 319 



rity in the arrangement of the teeth affected their position, 

 and these irregularities seem at least as common in the an- 

 terior as in the posterior portions of the jaws. It is not un- 

 worthy of remark, however, that in the jaws of these ancient 

 :reptiie fishes, as in the jaws of their modern representative, 

 considerable irregularities did occur, and that these occasion- 

 ally present to the palaeontologist appearances suited to puzzle 

 and mislead. Not only do we find recipient pits in a speci- 

 men, with no reptile teeth growing up beside them, — indi- 

 cating, apparently, that there were teeth in the opposite jaw, 

 upper or nether, which the jaw in the specimen wanted ; 

 but in other cases, the seemingly too wide socket, one-half 

 of which usually remains a recipient pit, is occupied to the 

 full by a second tooth, growing up so close beside the ordi- 

 nary one, that their points are in some instances scarce a line 

 apart. And so extraordinary is the appearance of these 

 double teeth, that it has been sometimes asked whether they 

 ought not to be regarded as bearing the stamp of specific pe- 

 culiarity. Of these double teeth, some very fine specimens 

 have been found during the last few years in the Carboni- 

 ferous ironstones of Gilmerton. Even where most remark- 

 able, however, I infer from my specimens of jaws of Astero- 

 lepis that they merely indicate individual, not specific pecu- 

 liarities, in the fishes to which they belonged. Among the 

 specimens on the table there is a beautifully preserved jaw 

 of a small Asterolepis, — which I owe to my friend Mr Dick, 

 — in which the anterior reptile tooth is, as in some of the 

 Holoptychii (jRhizodus) of Gilmerton, a double one ; but, as 

 shown by an examination of the entire fossil, the fish to which 

 it belonged did not differ in species from those which owned 

 several of the other jaws before us, all of whose anterior teeth 

 are single ones. [Spec. 2.] The double tooth, notwithstanding 

 its striking appearance, was as much an individual peculia- 

 rity, and as little a specific one, as those dental irregularities, 



I 



