15 



cover of the Derwent Grilse, including, of course, the prceo- 

 perculum, agrees admirably with the figure given by Yarrell, 

 as the gill cover of Sal mo solar. The Derwent Grilse is not 

 sufficiently mature to make the width and strength of the 

 maxillary of more than doubtful value, as a means of identify- 

 ing species. 



The vomerine teeth are rarely all absent from the mesial 

 line of a salmon trout till after the second or third trip to sea, 

 when it has attained a greater size than that of the Derwent 

 Grilse, in which all these teeth are wanting, as in the true 

 salmon after its first trip seawards. 



The caudal fin of the Derwent Grilse is distinctly emargin- 

 ate, whilst in salmon trout over 18 inches in length, this fin 

 is almost invariably square or rounded. The number of scales 

 in a line from the back of the adipose fin obliquely forward to 

 the lateral line, is in the salmon trout 14 or 15 ; in the 

 Derwent Grilse, it is 12 as in the true salmon, this, according 

 to Dr. Giinther, is one of the most constant characters, and 

 therefore of the utmost importance in determining the species. 



The number of the vertebrse and of the pyloric appendages 

 could not be correctly ascertained without disfiguring the 

 specimen which the Commissioners were loth to do. 



To sum up then. The Derwent Grilse must be one of the 

 two migratory species, Salmo salar, the true salmon, or Salmo 

 irutta, the salmon trout. In the variable characters it agrees 

 with the majority of specimens of salmon, better than it does 

 with the majority of specimens of salmon trout. In all of the 

 constant characters in which it has been tested, it agrees 

 absolutely with Salmo salar and differs absolutely from Salmo 

 irutta. In the face of such facts can there be any doubt that 

 the Derwent Grilse is really that which the Salmon Commis- 

 sioners have pronounced it to be, a true salmon {Salmo salar) 

 in its grilse stage ? 



And now let us see how the life history of the fish in this 

 colony goes to confirm the Commissioners in their decision. 



In April, 1864, the first salmon ova arrived in Tasmania and 

 and with them a few ova of the common trout, no salmon trout 

 ova being included in that shipment. In the Spring of 1865, a 

 number of smolts, estimated at about 1,500, from that ova, 

 went to sea, and at the same time 30 common trout were 

 liberated in the River Plenty, the whole of the remaining 

 common trout (about 150) being retained in a breeding pond. 

 In the following spring of 1866, the remainder of the smolts 

 from that first shipment, about 1,000, took their departure, 

 and in February, 1867, the Superintendent at the ponds, Mr. 

 Win. Ramsbottom, reported that he had seen several grilse, 

 which he estimated to weigh about 5 lbs. each in the fresh 



