14 ME. F. DAT ON TAEIATIONS IN FORM 



from carefully watching and noting the progeny of these fishes 

 when introduced into the Antipodes by means of ova sent from this 

 country. 



It has seemed to me very desirable that we should likewise 

 ascertain whether any changes occur in exotic forms acclimatized 

 in Great Britain ; and I have been especially anxious to watch 

 the American brook- trout (really a charr), Salmo fontinalis. This 

 fish is distinct from our common trout not merely in its colours, 

 but also in the number of scales along its sides, having many 

 more rows descending to the lateral lioe, while it possesses no 

 teeth along the body of the vomer, but merely a patch or trans- 

 verse band of from four to eight, situated opposite the conjunc- 

 tion of the palatine arch with the vomer. 



Eor opportunities of making the following comparisons I have 

 to thank Sir Pryse Pryse, of Goggerdan, Cardiganshire, Sir J. 

 Gibson-Maitland, Bart., P.L.S., of Craigend near Stirling, and 

 Mr. J. Carrington, P.L.S., of the "Westminster Aquarium. Por 

 the American specimens I am indebted to Professor A. Agassiz. 



I propose dividing the substance of my present paper under 

 the following heads, each of which will require a short notice : — 

 (1) The appearance of Salmo fontinalis as existing in its native 

 country ; (2) As living in this country in a wild condition in 

 streams ; (3) As kept in ponds into or through which there is a 

 plentiful supply of running water ; (4) As retained in aquaria 

 where the water-supply is small ; (5) Hybrid examples. 



(1) The appearance of the American brook-trout has been so 

 often described that recapitulation here appears to be unnecessary. 

 I have found 57 vertebrae, and the anal rays from 2-3/7-8. The 

 number of scales varies very considerably in the enumerations 

 given by different authors, due to the two modes of counting in 

 force. In one only the pierced row of scales along the lateral line 

 is taken ; and these vary from 115 to 140. But some ichthyolo- 

 gists assert that 200 or more rows exist along the lateral line ; 

 this is due to their counting the number of rows of scales passing 

 down from the back and falling upon the lateral line. In a very 

 well preserved male example in spirit in the British Museum 

 from Lake Superior, 12| inches in length, the head is 4| in the 

 total length, while the subopercle is nearly square, and the csecal 

 appendages are said to number 34. 



(2) What are the appearances of this fish living in this country 

 in a wild state in streams ? It is diflficult to answer this ques- 



