.] Recent Literatiiyc. 



103 



conditions, a common stock often runs into numerous well-marked oft- 

 shoots, the extremities of which differ much from each other, and which, 

 in their extreme phases, present no difficulties of recognition or char- 

 acterization, but which insensibly merge together at certain points within 

 the general habitat. These various forms are obviously the result of 

 differences in the environment — incipient species, instructive facts, links 

 in the chain of evolution, demanding a means of expression to which the 

 trinomial system is readily subservient. Each well-marked physical 

 region of a continent has generally a more or less well-marked form, 

 which it seems profitable to recognize by name, the degree of differentia- 

 tion of course varying with the placticity of the species. It at present 

 seems sufficient to recognize such forms as are correlated with certain 

 more or less definite or natural geographical and climatal areas. 



These remarks are suggested by the large number of species and sub- 

 species of late described from the southern border of the United States 

 and the contiguous region southward. A conservative person, judging 

 these forms by the descriptions, feels naturally some bias against them, 

 and is inclined to consider them as cases of too fine splitting, but later, 

 when confronted by the evidence afibrded by the actual specimens, is 

 obliged to admit that the alleged differences are not imaginary, and 

 that we have, in short, really a new 'fact,' requiring a 'handle.' This is 

 an experience to which even the writer of this notice is willing to confess. 

 In some instances the 'types' of newly described forms have been in some 

 of our leading collections for a generation, awaiting the accumulation of 

 material sufficient to reveal the significance of certain differences, perhaps 

 long before recognized but not understood. The true explanation of the 

 recent increase of new forms is in part the accumulation of material from 

 hitherto imperfectly explored fields, or from localities not before examined, 

 and the careful collation of the spoils thus gathered. The work of Mr. 

 Sennett in Texas is strikingly in point, where novelties never dreamed of 

 are rapidly coming to light, and quite revolutionizing our notions of the 

 Texan ornis ; while Mexico comes into view as almost an ornithological 

 El Dorado. 



In the Appendix to the new 'Key' Dr. Coues perhaps intends to enforce 

 the lesson of his preface, as well as to record his dissent (see p. iii of 

 preface) respecting the status of certain forms admitted to the A. O. U. 

 Check List, and as his judgment on forms since described. The revision 

 thus made, we are compelled to say, strikes us as rather offhand, and as 

 made in the library, rather than with specimens of the forms in question 

 actually under examination, — a rather unsafe proceeding in the present 

 state of the subject, and one tending to inconsistency in results. About 

 twenty species included in the 'Check-List' are not recognized in the 

 'Key,' three or four of which appear to have been rejected as being doubt- 

 fully North American, and the rest as not entitled to recognition. On 

 the other hand, about ten are included which the A. O. U. Committee 

 deemed it best to omit, and about seventeen others which they relegated 

 to the 'Hypothetical List.' with which reference we presume Dr. Coues 



