1920] Swarth: Revision of Avian Genus Passerella 79 



two or more adjacent forms. Many of these intergrades for con- 

 venience may be referred with some degree of assurance to the form 

 they most closely resemble, but many specimens fall so near the 

 imaginary line between two or more subspecies that it is practically 

 impossible to classify them other than as intergrades." 



It must not be assumed from the above statements that I am 

 dubious of the validity of the subspecies so far described. Far from 

 it. Each of them is readily apparent in typical form, and certainly 

 deserving of nomenclatural recognition. In the course of this study 

 it has been considered necessary to supply names for races not here- 

 tofore recognized but quite as distinct as some of older standing. 

 Furthermore, it would have been possible to have bestowed some 

 additional names, as will be seen in discussions of specific cases farther 

 on, but it did not seem to me that I should be justified in doing so 

 at the present time. It is thus evident that this study of Passerella 

 is not presented as the final word on the subject. In fact, it has become 

 clearly apparent that, abundant as the available material has been, 

 compared with what previous students of the group have had, some 

 future worker should certainly take up the subject with the advantage 

 of vasth' more extensive series. I am quite convinced, however, that 

 whatever changes such future reviser may advance, he will not reduce 

 the number of subspecies now recognized. I am inclined to believe 

 that this future student will adopt an attitude similar to that assumed 

 by Sumner (1918, p. 184) in one of his studies on variation and 

 heredity in Peroniysciis manicuJatus: "I am not in the least con- 

 cerned with characterizing and defining those taxonomic groups which 

 have been called Peromyscus maniculatus gamheii, riibidus and 

 sonoriensis. I shall merely discuss the differences between (and 

 within) four representative collections taken by me in widely sep- 

 arated and climatically different regions of the state. The question 

 as to what 'subspecies' a given mouse 'belongs to' is for my purposes 

 a distinctlj^ minor consideration." 



With a thorough appreciation of this method of treating the finer 

 divisions of a species, in the lesser degree of separation used in the 

 present study of Passerella iliaca it seemed advisable to attach a name 

 to each skin. The necessity of cataloging museum specimens impels 

 such action even were there no other reason to do so. It must be 

 evident, however, that in the present case (the treatment of Passerella 

 iliaca) the usage of this system of nomenclature is purely an artificial 

 contrivance, just such an aid as the drawing of checkerboard squares 



