NATURAL SCIENCES OF PHILADELPHIA. 53 



Simorhjjnchus aleutkus, Schlegel, Urinatores Mus. Pays-Bas, ix livr. 1867, p. 26. 

 Mergulus Cassinii, Gambel, Pr. A. N. S. Philada. ii, 1845, p. 266. Id., Jouru. 



A. N. S. Phila. 2d series, ii, 1850, pi. vi. 

 Arctica Cassinii, Gray, Gen. Birds, iii, 1849, p. 638. 



Pacific coast of North America, south to San Diego, California. Breeds on 

 the Farralone Islands. Aleutian Islands (Pallas), Russian America, and whole 

 west coast of the United States. (Mus. Smiths. Inst, and Acad. Philada.) 



Adult.— B\\\ black, base of lower mandible whitish or yellowish. Legs 

 anteriorly, and toes superiorly bluish ; legs posteriorly, and toes inferiorly, 

 with the membranes, blackish. A slight touch of white about the eyes. En- 

 tire upper parts blackish-plumbeous, the head, wings and tail nearly black. 

 This color, gradually diluted until it is much more grayish-plumbeous, ex- 

 tends around the under parts and sides of the head, the throat, upper part of 

 the breast, and whole sides of the body under the wings. Greater part of 

 breast, with abdomen and under tail coverts pure white ; the grayish plum- 

 beous of ihe upper breast merging very gradually into the white of the belly. 

 Under surface of wings dark lustrous gray. 



Young. — Very similar to the adult ; differing chiefly in being more decided- 

 ly blackish on the upper parts. 



Moulting specimens have the upper parts much duller and grayer, the old 

 wing and tail feathers faded, especially towards their tips, into light brown- 

 ish-gray. 



Length 8-00 to 9-50; extent 16-00 to 18-50 ; wing 4-75 to 5-25 ; tail 1-50 to 

 1 75 ; tarsus about 1-00 ; middle toe and claw 1-40 ; outer do. 1-30 ; inner do. 

 1-10; culmen -75 ; rictus -90; gonys -60 ; depth of bill opposite posterior ex- 

 tremity of nostrils -40 ; width -30. 



As regards color, this species is remarkably constant. Hardlj- any other 

 differences than those first noticed are to be found, after examination of exten- 

 sive series ; and they may all be summed up as merely varying shades of the 

 same color, and slight variation in its extent downwards upon the breast. The 

 bill at all ages and seasons presents its peculiar parti- coloration. These re- 

 marks, however, probably do not apply to fledgelings. As regards size, the spe- 

 cies is perhaps unusually variable, as may be seen by the measurements given 

 above, which represent extremes in those cases where two sets of figures are 

 given, and the average in other measurements. The bill, in particular, is 

 liable to great variation both in length and in stoutness. Some bills are very 

 large and robust, nearly as wide as high at the base, rather obtuse at the tip, 

 and with decidedly curved culmen and gonys ; others are longer in proj)ortion 

 to their transverse dimensions, decidedly compressed throughout, acutely 

 pointed, with almost straight culmen and gonys. The corrugations about the 

 base of the upper mandible are sometimes nearly obsolete, and when present 

 are very variable in character. Very likely they are hardly, if at all. apparent 

 in life ; for they seem to be produced mainly by the shrinking in drying of the 

 skin covering the nasal fossje and base of the culmen. All the variations ex- 

 hibited bj' the numerous specimens seem to be merely individual differences, 

 and are not sufficient to excite a suspicion that more than one species is repre- 

 sented in the series. 



Mergulus Cassinii Gambel (Arctica Cassinn Gray) is now well known to be 

 this species, first described by Pallas, as above quoted The species has no 

 other synonyms of consequence. Its striking peculiarities suffice to prevent 

 misconception regarding it. 



Subfamily URiNiE. 

 MERGULUS, {Ray) VieiU. 



Mergulus, Ray, Syn. Av. Vieillot, Analyse, 1816, and of authors. Type Alca 

 alle, Linn. 



1868.] 



