558 PROCEEDINGS OF THE ACADEMY OF 



Gavia fusca, Briason, Ornith. pi. xviii. fig. 2. 



Sterna stolida, Linn., S. N. 1766, i. 227, et auct. antiq. 



Anous stolidus, G R. Gray, Gen. Birds, 1849, iii. 661, et auct. recent. 



Megalopterus stolidus, Keys, et Bias., Wirb. Eur. 1840, 98. 



Anous niffer, Stephens, Gen. Zool. 1826, xiii. 140. 



A comparison of the Floridan bird with that from the South Pacific, collected 

 by Wilkes' Exploring Expedition, shows some differences of color, form and 

 size, which, though not great, are well marked and quite constant in all the 

 specimens I have examined. The bill of the Pacific bird is of the same length 

 as that of the American, but is higher at the base, which gives it a somewhat 

 different shape. The toes are considerably longer, while the tarsus is of just 

 the same length ; making a different relative length of tarsus and toes. The 

 wing is from a half to three-fourths of an inch longer ; the tail is very decidedly 

 longer, the difference being quite an inch. The central tail feathers are half an 

 inch shorter than the lateral leathers in the Pacific bird ; while in the American 

 the emargination is much less, only about a fourth of an inch. The differences 

 in color are slight. The American bird has the occiput bluish plumbeous, 

 which fades into pure white on the crown anteriorly; while the Pacific bird 

 has the occiput darker, and the crown ashy white instead of pure. The sides 

 of the head and neck all round, in the American bird, have a bluish plumbeous 

 wash, notably different from the general fuliginous, which is entirely wanting 

 in the Pacific bird. The feet of the American bird appear much darker in the 

 dried skin. 



Mr. Cassin, in the Ornithology of the Expedition, remarks upon these differ- 

 ences in the following words: "Numerous specimens from the shores and 

 islands of the Pacific Ocean present, with some degree of uniformity, small and 

 apparently unimportant differences from others from the Atlantic coast of North 

 America. The bill appears to be larger in the latter, and a slight dissimilarity 

 is observable in the colors. On careful comparison, however, we are not in- 

 clined to consider the bird of the Pacific as possessing characters sufficient to 

 justify a distinct specific designation ; but venture to suggest that further 

 examination of specimens from localities in the two great oceans, and especi- 

 ally of the various immature plumages, is yet desirable." 



I tabulate the differences between the two, leaving it to future investigation 

 to determine their constancy and value. 



American Bird. 



Length of wing 10-00 to 10-50 inches. 



Length of tail about 6-00. 



Height of bill at base -38. 



Length of tarsus 1 00. 



Length of middle toe and claw 1 45. 



Middle toe and claw 1-45 hundredths 

 of tarsus. 



Central tail feathers but slightly 

 shorter than the next. 



Occiput bluish plumbeous, becoming 

 pure white on the front. Sides of head 

 and neck all round with a decided 

 wash of bluish plumbeous. Feet nearly 

 Dlack in dried skin. 



Pacific Bird. 



Length of wing 11-00 to 11-25. 



Length of tail about 7-00. 



Height of bill at base -43. 



Length of tarsus 1*00 (same). 



Length of middle toe and claw 1-60. 



Middle toe and claw 1-60 hundredths 

 of tarsus. 



Central tail feathers -50 of an inch 

 shorter than next. 



Occiput brownish ash, becoming ashy 

 white (not pure) on the front. Sides 

 of head and neck not notably different 

 from general fuliginous. Feet reddish 

 brown in dried skin. 



The difference in color appears very slight. I attach more importance to the 

 discrepancies in size and proportions. If the Pacific bird be really distinct 

 from the American, it has probably yet to receive a name ; for it is very differ- 

 ent from the various species of Anous mostly described by Mr. Gould. In that 

 event, it may be called a Anous frater. 



In the preceding pages are noticed all the Terns which are known 10 inhabit 



[Dec. 



