138 PROCEEDINGS OF THE ACADEMY OF 



robust bills, somewhat longer and more pointed wings, etc. These latter 

 characters have been made typical of a distinct genus by Bonaparte. The 

 gradation, however, in these and all other features is so gradual, through 

 several intermediate forms, that I do not see how we are to draw the dividing 

 line. Bonaparte moreover includes in CooMlaria such a species as Solandri, 

 which is particularly a robust bird. 



Throwing out of consideration the fuliginous " Pterodromine " group, we 

 find that the other species of yE<trelata adhere quite closely to a particular pat- 

 tern of coloration. When adult they are dark colored above, being of some 

 shade of brown or black, with more or less of an admixture of cinereous, and 

 generally have a white forehead. The color of the upper parts extends on the 

 sides of the breast ; otherwise the under parts are wholly white. When 

 young, the color of the under parts does not diifer very notably as a general 

 rule from that of the upper: the white being obscured by a dusky, fuliginous 

 or cinereous clouding of the tips of all the feathers, the basal portions of which 

 remain white. In general the younger the bird the more uniform, or more 

 tending towards fuliginous are its colors: while in adult life light and dark 

 colors occupy distinct areas, and are quite trenchantly defined. 



When we consider, therefore, the great change which the plumage under- 

 goes in the bird's progress towards maturity, together with the similarity 

 that exists between corresponding ages, it will not appear surprising that not 

 only very numerous nominal species should have arisen, but that names of 

 species should have been frequently misapplied to others than those to which 

 they rightly belong ; producing a confusion in the synonymy certainly not 

 surpassed, if indeed equalled, in any other penus in ornithology. A number 

 of the species were first brought into notice by voyagers ; and when named by 

 professed naturalists it was at a time when the neces-ity of detailed descrip- 

 tions was not appreciated, so that the nice points of size and proportion which 

 really distinguish the species more than colorj were rarely presented. The 

 consequence is that it is now impossible to identify many of the older names 

 with any degree of certainty, except perhaps by incidental or collateral testi- 

 mony ; and to this day a great many identifications remain matters of opinion 

 rather than of fact. 



Nor is the confusion and uncertainty by any means less in the fuliginous 

 group which goes to compose this genus. Its components, so far as we know, 

 are in every age unicolor ; and are absolutely indistinguishable except by 

 form and dimensions. This alone would have been amply sufficient for the 

 production of synomyms and malideutifications innumerable ; but this inevi- 

 table result is furthered by another fact. The " genus " Pterodruma is among 

 the JEstrelatea exactly what Nectris is among the Pajfinetv ; i. e. composed of 

 species differing in no wise in form from ^Ettrelata or Puffinus, and which are 

 entirely fuliginous in color. Now the points of form separating the species of 

 " Pterodroma " from " Nectris " are by no means patent on a casual examina- 

 tion ; and hence, among the older writers we find many descriptions which 

 it is impossible to refer with any degree of certainty to one or the other genus, 

 of which, in short, we can say no more than that a fuliginous petrel formed 

 the subject of the article. Consequently, some synonyms have ever been oscil- 

 lating as to weight of authority between these two groups. 



I confess to a feeling of surprise, when, on examining critically species 

 typical of Bonaparte's genus Pterodroma, I could find absolutely no points of 

 form whereby it might be held separable from ^Estrela'a. I do not think that 

 the skeleton will be found to present any tangible morphological characters, 

 critically examined in its minutest details of intermaxillary bone or phalanges ; 

 nor do the remiges or rectrices in their relative developments offer the 

 slightest discrepancies. We mu*t have recourse therefore to color alone if we 

 would separate them ; aud Bonaparte himself gives us no other character 



