542 PROCEEDINGS OF THE ACADEMY OF 



Th. acuflavidus. — White margins of inner web of three or four outer prima- 

 ries narrow, falling short of tip, which is wholly occupied by the black portion. 

 Breadth of white margin 11 inches from tip of first primary, -10 of an inch. 



Genus STERNA Linnaeus. 



Sterna, Linn., Syst. Nat. 1748. Type, S. hirundo, Linn. 



Tkalassea, Kaup, Sk. Ent. Eur. Theirw. 1829, p. 97. Type, S. paradisea, Briin. 



Hydrocecropis, Boie, Isis, 1844, p. 178. Type, ? (includes S. paradisea.) 



Slernula, Boie, Isis, 1822, 563. Type, S. minuta, Linn. 



Ch. — Head without a decided occipital crest, but the feathers of the parts 

 somewhat elongated; size moderate, or very small; general form slender and 

 graceful. Bill about as long as, or slightly shorter than, the head, greatly ex- 

 ceeding the tarsus ; of varying stoutness, but usually quite slender, very acute, 

 the culmen gently curved, being slightly declinato-convex. Commissure gently 

 curved ; outline of rami a little concave, of gonys quite straight, the angle at 

 symphysis well marked and acute, but not very prominent. Wings long and 

 pointed. Tail of variable length and amount of forfication, but always de- 

 cidedly greatly forked ; the lateral feathers elongated, slender and tapering, 

 greatly sui passing the others. Tail contained in the wing of the type of the 

 genus about 1| times; in arctica 1| times; while the tail of paradisea is bat 

 little less thfm the wing. Tarsus slender, slightly shorter than the middle 

 toe and claw, slightly longer than the middle toe alone ; much shorter than 

 the bill, about equal to the distance between the projection at symphysis and the 

 tip of the inferior mandible. 



The genus Sterna, in the restricted acceptation in which it is employed by 

 most modern authors, embraces quite numerous species, all more or less inti- 

 mately related to S. hirundo. The group is one well defined, its species agree- 

 ing very closely in size, general form, pattern of coloration, and seasonal 

 changes of plumage. Specific characters are generally found in the varying 

 length and stoutness of bills and tarsi, amount of forking of the tail, markings 

 of the primaries, and other less decided features of coloration. 



Sterna proper has comparatively few synonyms, the principal of which are 

 those given at the head of this article. Thalassea, Kaup, and Hydrocecropis, 

 Boie, are strictly synonymous, while Stermila, BAe, is based upon a species 

 differing but very slightly from the type, S. hirundo. 



"Sterna Trudeaui Aud." 



Sterna Trudeaui, Audubon, Orn. Biog. v. 1839, 125. Lawr. Gen. Rep. Birds, 

 1858, 861. 



I have before me a typical specimen of Sterna Trudeaui, belonging to J. P. 

 Giraud, Jr., the one from which was drawn up the description in the General 

 Report, and supposed to be also the original of Audubon's plate and descrip- 

 tion. As these are the chief descriptions of the bird which have ever appeared, 

 and as, I believe, the specimen is the only one known to exist, it may fairly be 

 considered to embody all that is at present known of the species. From the 

 peculiar characters presented by it, as well as by the species which succeeds, 

 — to both of which attach, for various obvious reasons, doubts as to validity, 

 — it may be of advantage to e.xamine somewhat closely into its charac- 

 ters, to determine if possible whether they be distinct from each other ; and in 

 that case in what they differ from 5. Forsteri. 



The bill is quite stout at the base, both as regards height and width, and 

 tapers regularly to an acute point, the culmen being but slightly arcuate. It is 

 precisely the length of that of an adult Forsteri, and also of a supposed HavelU.* 



*The specimens of-' Uavelli" referred to, are those furnished by Mr. Lawrence, and no labelled 

 t,y him. 



[Dec 



