722 COLYMBUS ARCTICUS, BLACK-TIIROATED DIVER. 



l)lack, these stripes nearly meeting; in front. Entire upper parts deep, glossy grecuish- 

 blac!<, eacli feather of scapniars and interscapulars with a white spot near end of each 

 web ; those of the scapuhirs largest, forming four patches in transverse rows. Wing- 

 coverts thickly speckled with small ovate white spots. Inner webs of quills and tail 

 feathers below, light grayish-brown. Sides under wings like back. Lining of wings 

 and entire under parts from the neck, pure white, with a narrow dusky band across 

 lower belly ; under tail-coverts dusky, tipped with white. 



Youufj.— BUI light bluish-gray, dusky along the ridge. Iris brown. Feet dusky. 

 Upper part of head and neck dark grayish-brown ; sides of head dark grayish-white, 

 minutely streaked with brown. Upper parts with a reticulated or scaly appearance, 

 the feathers being brownish-black with broad bluish-gray margins ; the rump dull 

 brownish-gray. Primaries and their coverts brownish-black ; secondaries arul tail 

 feathers dusky, margined with gray. Forepart of j]eck grayish-white, n)inutely aud 

 faintly dotted with brown ; its sides below streaked with the same. Lower parts, in- 

 cluding under surface of wings, pure white, the sides of the body aud rump, with jjart 

 of the lower tail-coverts, dusky, edged with bluish-gray. (Aitduho7i.) 



Dimensions.— Wing, 1L75 ; bill along culmen, 2.45 ; along gape, 3.40 ; its height at 

 nostrils, 0.65 ; its width there, 0.35 ; tarsus, 2.90 ; outer toe and claw, 3.H0. 



The foregoing description is taken from a fine adult European specimen, no unques- 

 tionable North American one being before me. The account of the young is derived 

 from Audubon. I am not sure that I have recognized it from North America, the young 

 of the arciiciis type before mo being apparently all var. pacijicus. It may be distin- 

 guished from the young of torquatas by its decidedly inferior size. The questions 

 arising from consideration of var. xMclfiGus are treated under the next head. 



Yar. PACIFICUS : Pacific BlacTc-throatcd Diver. 



In 1858 Mr. Lawrence separated, "with some hesitation," two specimens of the 

 arcticiis typo from that species, under the name of paciftcus, on the ground of smaller 

 s'ize, and especially smaller, weaker bill. A young bird iu the Philadelphia collection, 

 "which may have come from the Pacitic," being exactly like the types of j>flc(/(CHs; 

 and the fact that young arcticus is described as closely resembling young (orqiiatiis, 

 whereas the types oi pacificus are quite different, strengthened the opinion that pacijicus 

 ■was distinct, and I so treated it in 1862. But now, with Mr. Lawrence's types and 

 several fully adult specimens before me, I reduce the differences merely to a point of 

 size, which, as is well known, is very variable iu this family. The bird is evidently 

 only a slight variety, as will be perceived by the following examination of specimens : 



No. 21795, Mus. Smith. lust., adult, Europe : Bill moderately stout, little compressed, 

 shorter than head or tarsus, tip rather acute, culmeu regularly convex throughout, 

 commissure greatly decurved, under outline straight to the angle, gonys straight, angle 

 well detined. Culmen, 2.45 ; g-ape, 3.40 ; height at nostril, 0.65 ; width there, 0.35 ; 

 ■wing, 11.75. 



No. 16014, adult, Eraser's River, collected by Dr. Kennerly on the Northwest Bound- 

 ary Survey: Apparently pure arcf(Vi(s. Wing, 11.75; tarsus, 2.90 ; outer toe, 3.80 ; thus 

 fully as large. The upper mandible is shot away from the nostrils, but according to 

 the under mandible the bill was 0.25 shorter than iu the preceding ; its height at base 

 is the same. 



No. 17052, intermediate in age, California : Smaller. Wing, 11.30; tarsus, 2.85; outer 

 toe, 3.55 ; culmen, 2 : gape, 2.90 ; height of bill at base, 0.48. The bill is considerably 

 shorter and slenderer than in the European ; the culmeu decidedly convex ; gonj's 

 convex. 



No. 20229, adult. Great Slave Lake : Smaller than either of the preceding. Wing, 

 only 11 ; tarsus, 2.60 ; outer toe, 3.00 ; culmen, 2.05; gape, 3.20; height of bill at base, 

 0.50. The bill thus differs little from the preceding. 



No. 9924, voung, Puget's Sound : A type of the species ; about the size and propor- 

 tions of 17052. Wing, 11.20; tarsus, 2^80; culmen, 2.12; gape, 3; height, 0.50. This 

 hiis the bill a little larger than in 17052, the culmeu considerably curved, the gonydeal 

 angle pretty well deliued. (Difference in length of culmeu between this aud the Eu- 

 ropean specimen, aliout 0.30 ; the wing only 0.75 shorter.) 



No. 20231, adult, M'Kenzie's River : Small. Wing, barely 11 ; tarsus, 2.50 ; outer toe, 

 3.50; culmen ovly 1.90; height of bill, 0.45. This has the smallest, straightcst. and 

 slenderest bill of all. The culmeu is even a little concave at the nostrils ; commissuio 

 jierfectly straight ; gonydeal angle slight. Were this shape aud size of bill constant, 

 a species might be jiredicated. 



No. 11862, young, Eraser's River : Smallest of the specimens. Wing, 10.75; tarsus, 

 2.75 ; outer toe, 3.80 ; culmeu, 2 ; gape, 2.85 ; height of bill, 0.45. The bill resembles 

 some others of the foregoing more thau it does that of 20231. 



The complete graduation is established by the above series, showing that we can only 

 recognize a var. pacificiis as one extreme of au unbroken chain. 



