There is one flycatcher respecting which we are in doubt, and which was very abundant this spring. It is the one we had considered _M. Pusilla_ but a thorough examination of the Biography, has thrown doubt on this supposition, it agrees pretty well with the _M. Acadica_ of Nuttall, but not with the _Acadica_, of the Synopsis. I will send you one as soon as possible, as there is no set of Plates in Carlisle to which we might refer. In conclusion Baird added: "May we not expect to see you in Carlisle before a great while? It would give us very great pleasure indeed." Though Audubon gladly admitted this new-found species of bird at a later day, he was not at first disposed to accept its validity, as will appear in the following interesting letter which he sent to his young friend: _Audubon to Spencer Fullerton Baird_ NEW YORK, _July 29, 1841_. MY DEAR SIR,— I have not had time to answer your interesting favor of the 21st until this morning, being now constantly engaged in the figuring, &c., of the Quadrupeds of Our Country; by which I mean that I actually work from daylight every day until I retire to my necessary repose at night. Your observations upon the birds of passage the last spring are what they have been almost throughout the U. S. The very backward spring which we have experienced this year did no doubt retard the coming into the States the millions of passenger birds that come to us from beyond our limits. The Fly-catcher of which you are in doubt is nevertheless the _M. Pusilla_, and you must not be surprised to find _perhaps_ some discrepancy between the specimens you have procured and the descriptions you may have read, as among mine these differences are quite obvious and belonging to either sex or age, as is indeed the case with most of our birds as well as among many of our quadrupeds.... I cannot at present tell you when I may have the pleasure of meeting you at your own domicile, and yet this may happen quite unexpectedly. Do you pay attention to the quadrupeds around you? If not, I wish you would!—and moreover I should be highly pleased to hear of your procuring for us all such as may be found in your vicinity. You have _Bats, Wood Rats, & Mice, Weasels, &c., &c._, all of which I should like to possess specimens at your hands. Could you not save all that you come across with in this way, place them in _common good Rum_, and forward them to me at once or as soon as you have some 2 or three species. I will most cheerfully pay all expenses to Philadelphia addressed to _J. B. Chevalier_, No. 70 Dock Street.