LETTERS FROM DR. HARRIS. 189 



when the fin is not fully stretched. Again, the lower jaw 

 of Boreus, judging from the figure, is less prominent. The 

 squamation of the cheeks and operculum is also very pecu- 

 liar in Boreus; but since you do not mention this character 

 you may, in that respect, compare your fish with my descrip- 

 tion to complete the specific difl"erences. 



I have distinguished several other species of Esox, some 

 of which were figured in Frank Forrester^s Angler^ but 

 the author, Mr. Herbert, unfortunately transposed the 

 names, a mistake which Mr. F. Thompson has justly noticed 

 in his Appendix to the History of Vermont. You will also 

 see that he has identified his Salmo perca with my Percopsis. 

 When I saw the only specimen he had, I paid very little 

 attention, and indeed did not remember his fish when I 

 found and described my Percopsis, otherwise I would have 

 alluded to it. I have not yet had an oj)portunity of satis- 

 fying myself of the specific identity of the two, from want 

 of specimens from Lake Ohamplain. 



Many thanks for the Report. I am delighted at the pros- 

 pect of obtaining the fishes of your vicinity, after so many 

 failures, and trust it may be the foundation of a more regu- 

 lar intercourse between us. 



Respectfully Yours, 



L. Agassiz. 



Dr. J. P. KiRTLAND. 



Cambridge, Mass., July 26, 1852. 



Prof. J. P. KiRTLAND : 



Dear Sir — It would give me much 

 pleasure to visit you at the time proposed, although I am 

 not a member of the Association, and I am strongly temi)ted 



