178 Bulletin American Museum of Natural History. [VoJ, XXXVI, 



In spite, therefore, of their non-intergradation, T feel that a knowledge 

 of their relationships is best conveyed by a trinomial; and such a designa- 

 tion in connection with a statement of their ranges, gives far more informa- 

 tion of this interesting case in distribution, than if the birds were treated 

 as distinct species. 



The third group contains forms so closely related that in many instances 

 their separation would not be suggested were their ranges not known to be 

 disconnected. Many island forms come under this category. Separated 

 from their mainland representative by a physical barrier which prevents 

 contact of their respective ranges, and hence geographical intergradation, 

 they are often classed as 'species' when the differentiating characters 

 ascribed to them are so slight as to be bridged by individual variation, 

 specimens occurring in the range of either form which might readily be 

 referred to the other. 



It is in the treatment of the fourlh group that the greatest difference of 

 opinion is manifest. Here differentiation has been carried too far to permit 

 of intergradation by variation, and geographical intergradation is prohibited. 

 Such forms therefore might appear to fulfil the requirements of species, but 

 I am convinced that in most instances to rank them as such is not only to 

 conceal the real facts at issue but to mislead by a false statement. 



An excellent illustration is furnished by that group of subtropical species 

 which inhabit the fountains of Colombia and are represented by closely 

 allied but well differentiated forms in the mountains of western Panama and 

 Costa Rica. Here the Tropical Zone is an actual barrier to contact of range. 

 Not only in the lower intervening tropical area, but in the region they in- 

 habit, these forms do not occur below a certain level. This discontinuity of' 

 range indicates almost beyond question the former connection of the now 

 widely separated subtropical portions of this mountain system, and is 

 consequently a physiographic and faunal fact of high importance. 



The zoological evidence involved can, however, be largely hidden by the 

 Use of a terminology which recognizes a purely artificial nomenclatural law 

 as of greater importance than an attempt to express, so far as the rules of 

 zoological nomenclature permit, the actual and undisputed facts in the case. 



An even more striking single case is furnished by the occurrence of a 

 form of the boreal species, Otocoris alpestris, on the Savanna of Bogota. 

 ■ Geographically the nearest known form of this species is found in southern 

 Mexico. Intergradation by contact for this plains-inhabiting species is 

 obviously impossible. It is too strongly differentiated to intergrade by 

 variation; it consequently conforms to the hard and fast definition of a 

 species, but to refuse to recognize its close relationship to Otocoris by classing 

 it as a subspecies of that group under a trinomial, is to, in part, disguise 



