lOO Reviezvs. f f"n\ 



^^^-^ |_2"Q Oct. 



specifically distinct. As in the case of genera, very different extremes 

 are often connected by a series of intergrading forms, approaching one 

 or the other of the extreme types exactly in proportion to their 

 geographical position between them ; and other forms much less 

 different appear to be really distinct through absence of ' intergrades.' 

 In determining questions of this class, the author has exercised the 

 fullest independence, without reference, so far as North American 

 forms are concerned, to the rulings of the committee of the American 

 Ornithologists' Union ; not from lack of confidence in the committee's 

 judgment, but from a full knowledge of the unsatisfactory conditions 

 as to time and material under which their conclusions were usually 

 reached. Satisfactory decisions affecting the status of described but 

 still dubious forms is a question both of material and investigation, 

 and the author holds that no conclusion in such a matter should be 

 accepted unless based upon an amount of material and careful investi- 

 gation equal to that bestowed by the original describer. 



" Recognizing the fact that in the present stage of zoological nomen- 

 clature trinomials are a ' necessary evil,' the author has not hesitated 

 to use them when such relationship was clearly indicated by the 

 evidence. He has not, however, often done so on theoretical grounds, 

 because, in the first place, the facts when known may or may not 

 justify the step, and in the second because a binomial is preferable 

 to a trinomial when there is any good excuse for its adoption. The 

 greatest difficulty in deciding questions of this kind is in the case of 

 insular forms, among which occur every possible degree of difference 

 between related forms inhabiting different islands, so that it not 

 only becomes largely a matter of individual judgment as to which 

 should be given specific and which sub-specific rank, but furthermore 

 the distinction made must, in the case of any author, necessarily be 

 more or less arbitrary, since no ' hard and fast rule ' for determining 

 such questions seems possible. 



" As observed before, the more familiar one becomes with the subject 

 through the medium of specimens representing continuous geographic 

 sequence of localities the fewer in number really distinct species become, 

 and what have long been considered such resolve themselves, one by 

 one, into a connected series of sub-specific forms, each representing a 

 definite geographic area of more or less marked peculiarites of topo- 

 graphy, climate, or other physical features. Such forms are fixed, or 

 ' true,' over territory of uniform physical character, the intergrades 

 coming from the meeting ground of two such areas. Such a group of 

 conspecific forms may aptly be compared to the colours of the solar 

 spectrum, which form a graded scale from red, through orange, yellow, 

 green, and blue, to violet, with intermediate hues of greater or less 

 number, according to the nature of the case requiring their indication 

 by name. These colours of the spectrum, though imperceptibly running 

 into one another, are obviously distinct, and the necessity of recog- 

 nizing them by name has never been questioned. 



" To carry the comparison still further, a certain species may include 

 six sub-species or conspecific forms, which for convenience inay be 

 designated by the sub-specific names rubra, aurantiaca, flava, viridis, 

 cyanea, and violacea. Intermediates between these might be designated 

 as rubro-aurantiaca (or auranitaco-rnbra , according to which form the 

 intermediate most resembles), aurantiaco-flava (or flavo-aurantiaca), 

 fiavo-viridis, viridi-cyanea, and cyaneo-violacea — i.e., red-orange (or 

 orange-red), orange-yellow (or yellow-orange), yellow-green, green- 

 blue, and blue-violet of the colour scale. The necessity for such a 



