88 



MR. F. DAT ON THE LOCIT-LEVEN TEOTJT. 



Leven trout, but in a double row in burn-trout of the same size, we 

 have first to consider whether the facts as stated are correct. All 

 trout and salmon (not charr) when young, irrespective of the teeth 

 on the head of the vomer, have a double row along its body ; but 

 these in all are dependent on age or rapidity of growth, and fall 

 out, commencing behind and extending forwards. In salmon and 

 sea-trout, which are forms that grow most rapidly, these teeth are 

 shed the earliest, while the Loch-Leven trout, which is likewise a 

 rapid grower, loses them rather sooner than the burn or loch 

 form ; hence to say that in the mature examples they are invariably 

 in a single row is erroneous. At the same time it is not here 

 advanced that rapidity of growth is the sole cause of this, for 

 the deciduousness of the teeth appears to be owing to the absorp- 

 tion or narrowing of the tooth-bearing ridge on the vomer, in 

 consequence of which the teeth, originally placed in pairs, become 

 ultimately ranged in a single row and finally fall out. 



The condition of the vomerine dental system in specimens of 

 Loch-Leven trout may be thus recorded : — (1) $ 20 inches 

 long, 2 teeth exist on the hind edge of the head of the vomer, 

 and 3 along the front half of its body, the first two of which 

 are almost opposite one another, (2) c? 9 inches long, 2 

 teeth at hind edge of vomer, 2 at the front end of the shaft, 

 and 7 in an irregular zigzag line, almost in one continuous row, 

 while their points turn alternately to the right and left. (3) $ 

 10*9 inches long, 2 at hind edge of head of bone, 2 in a line 

 at the commencement of the body, and 8 as in the last but more 

 distinctly in pairs. (4) $ 13*5 inches long, 2 at hind edge of 

 head of vomer, then 4 in a single row, next a pair turning one to 

 each side, and lastly 4 more single ones. (5) S 14 inches long, 

 2 teeth at hind edge of head of vomer, 9 in a single row along 

 the body of that bone ; of these the two central ones form a pair. 

 (6) 2 19"2 inches long, 4 teeth at hind edge of body of the 

 vomer, 12 along the body, among which are three pairs. (7) $ 

 23 inches long, 3 at hind edge of head of vomer, 8 along its body 

 in a single row, some turning one way and some another. 

 The foregoing seven specimens show that it is by no means an 

 invariable rule that all the teeth along the body of the vomer are 

 in a single row. 



Having examined a considerable number of burn or loch trout 

 in Sutherlandshire, I found that the maxillae were not stronger 

 than in the Lochlevens, while a specimen * taken at random 

 * Exhibited when the paper was read. 



