NATURAL SCIENCES OF PHILADELPHIA. 123 



General Considerations. 



Before proceeding to speak in detail of the individual species of the Lestri- 

 dinm, I desire to make a few remarks on the points which at the present day 

 must be taken more especially into consideration, in carrying on an investi- 

 gation of this subfamily of birds. 



Although the contrary was formerly the case, yet at the present time the 

 species of Jiigers are pretty definitely ascertained, being better known, in 

 fact, than the species either of Larince or Sternince. This arises partly from 

 the fact of the small number of existing species, and partly because most of 

 the species present really very marked differences, which can hardly be over- 

 looked by any one examining specimens with an ordinary degree of mental 

 acumen. With the amount of knowledge which we possess at present, it 

 would be quite impossible to mistake Buffoni for parasiticus, etc., in 

 whatever stages of plumage they may be found ; and therefore, except 

 in one or two instances, I have thought it quite unnecessary to present 

 any lengthy description or specific characters, for the purpose of separat- 

 ing one species from another. In a paper like the present, such points seem 

 quite uncalled for. 



At the same time, there is a point concerning which authors are even now 

 at variance, and which seems to have need of all the light that can be thrown 

 upon it. I refer to the remarkable changes of plumage which the species of 

 one of the genera of this subfamily, Stercorarius, undergo in arriving at 

 maturity, and more particularly that perplexing state in which the bird is 

 uniformly dusky. From the time when Briinnich, in 1764, institutes a 

 Catharacta " coprotheres, corpore toto fusco," etc., and then adds: "An a 

 prsecedenti sexu vel specie diversa ? A quibusdam hsec pro foemina, ilia 127 

 (parasitica) pro mare habetur, " the question has been an open one. Some 

 authors have made a distinct species of this stage ; others have given it as a 

 variety ; others still have considered this plumage indicative of age, or of 

 season, or of sex. Modern opinions have generally agreed in considering it 

 as simply an evidence of immaturity, and not a variety, much less a distinct 

 species. I hope I shall be able to show in the following pages, that this latter 

 opinion is the correct one, even if I cannot prove exactly what age the dusky 

 stage is characteristic of, or whether more than one sex participates in it. To 

 this end, I have gone into detail regarding the various ages of two of the 

 species, pomarinns and parasiticus. 



But there is still another point in the study of the Jiigers, which, being a 

 matter of more than ordinary difficulty, demands our most patient and 

 careful investigation. This is the bibliography of the subfamily. Many of the 

 species were known to the very earliest, even pre-Linnsean, writers on 

 ornithology ; and, as a natural consequence, the synonymy of the various 

 species is as intricate, and in as puzzling a state of complication, as perhaps 

 that of any other group of birds, rendering it a peculiarly difficult task to 

 unravel the various knotty points which present themselves for our considera- 

 tion. Fortunately, however, the synonymy of most of the species is rather 

 intricate, than doubtful ; rendering it possible, perhaps, to present a tolerably 

 accurate list of references, by careful and patient study. To this part of the 

 subject in hand I have paid special attention, and it is believed that the lists 

 of synonyms given are pretty full, and include all the important references. 

 Others must judge of the accuracy of the citations, each according to his own 

 views of the subject. 



If I seem to have made any uncalled for innovations in nomenclature, I 

 can only offer as an apology, that it is impossible to conduct an investigation 

 into the bibliography of the subfamily without seeing that many of the names 

 in common employ must be superseded, provided we are to pay any attention 

 to recognized laws of nomenclature. 



1863.] 



