NATURAL SCIENCES OF PHILADELPHIA. 51 



mere presence or absence, therefore, of the node upon the base of the culmen, 

 cannot be allowed to constitute a specific character in the present case, and 

 may be left out of consideration, as may be, also, the color of the bill. Too 

 much stress should not be laid upon the presence of white scapulars and of 

 white tips to the secondaries, since in some specimens of undoubted microce- 

 ros unmistakable traces of the former are to be found, and the ends of the 

 inner secondaries are decidedly lighter than the body of the feathers. All 

 the observable differences iu the quantity and distribution of the whitish se- 

 taceous feathers upon the forehead and other parts of the head might readily 

 enough depend upon a difference in the age of specimens. The pure unin- 

 terrupted white of the under parts of />i«/WMs stands in apparently strong con- 

 tradistinction to the black mottling of the same parts of microcerus ; but it is 

 to be remembered that the coloration in this respect of the latter species is 

 very variable, ranging from a very sparse and scanty marbling to a nearly 

 uniform black, particularly upon the breast, and is therefore not to be too 

 implicitly relied upon, at least until it is more definitely ascertained than at 

 present whether the black mottling tends to decrease or to increase with ad- 

 vancing age. If microceros grows more and more marbled with black as it 

 grows older, we might with entire propriety presume upon the existence of a 

 youthful state of plumage, in which the under parts are entirely white, like 

 those of pusillus. Such is very likely the real state of the case ; for the 

 youngest examples of microceros examined — those which have no trace of a 

 tubercle — are nearly white below, only very sparsely and indistinctly mottled 

 with blackish. Still, aside from all these varying and therefore uncertain 

 points, there appear good grounds for separating the two species, as will be 

 observed on comparing the descriptions given in this and in the preceding 

 article. 



As the case stands with our present information upon the subject, P. pusil- 

 lus is to be separated from F. microceros: first, by certain differences posi- 

 tively known to occur : or, in size, which is decidedly less, as evidenced by 

 the measurement of all its dimensions ; b, in form of bill, which is slenderer, 

 more acute at the tip, not so deep at the base, particularly not so wide at the 

 base, yet not shorter, than that of microceros ; secondly, by certain differences 

 very constantly observed, yet not proven to always hold good : a, absence of 

 tubercle; 6, conspicuously white scapulars and tips of secondaries: c, pure 

 white under parts, uninterrupted by blackish mottling, and extending around 

 on the sides of the neck; d, shortness and scantiness of the white setaceous 

 feathers on the forehead ; e, color of bill, mostly black, not mostly red. 



It only remains to notice the synonymy of this species , and all that is to 

 be said on this score relates to the identification of Alca pygmxa Gm. This 

 name is founded upon the "Pigmy Auk" of Pennant, — a small species first 

 described very loosely and imperfectly by the latter writer, whose account 

 Gmelin merely renders into Latin, in applying a binomial name. There is 

 no doubt that the bird was one of the little Auks of the North Pacific, as its 

 very name, and the dimensions assigned (seven inches), clearly indicate, but 

 there is no possibility, at the present day, of identifying it with precision. It 

 was very possibly based either upon the present species or the preceding 

 (microceros), and should these two ever be united, as young and old of the 

 same, the name pygmma might without undue violence be assigned to the 

 species so constituted. So long as they are regarded as distinct, the name 

 pyymxus must not be applied to either of them. As far as we can judge by 

 the description, particularly the expression "jugulo et pectore glaucis," 

 pygmxa may not impossibly have been based upon Ptychoramphus alevticvs. 

 But Mr. Gassin's supposition is perhaps as near the truth as any that could be 

 advanced: " It is possible that the Pigmy Auk of Pennant, which \& Aka 

 pygrmea Gmelin. may be the young of this species [_microcrros'\, but it is more 

 probable, judging fiom the descriptions of Gmelin and Latham, that several 

 small species have been confounded under this name." The same gentleman 



1868.] 



