706 HYDROCHELIDON LARIFORMIS, BLACK TERN. 



thfi sides of the head below the eyes and ear-coverts, the chin, throat, iiei'1< all round, 

 and the whole under parts, pure while. The under wiufr-coverts retain a good deal ot 

 their jdnnilieoiis hue. Tlie npjjer iiarts freiiniilly, and eN)icc,ia]ly the primaries, are 

 nineli as in MUiinier; hut the tint of the iihimhidiis, (■.sp( eially on the rump, i» consid- 

 erably lighter, and the feathers have faint whitish niarfjins. The hack hetween the 

 shoulders is considerably lighter tlian in summer, but a little darker than the rump. 

 Along the Ibje-aru], just beyond the whitish edge of the wing, there is a, rather broad 

 hand of grayish-black, formed by sevcial rows of the lesser coverts. Along the dorsal 

 aspeet of Uie arm, al.so, there is something of this black band, but the color is con- 

 cealed l->y the scapular featbc rs. Tlie hcroiidaries are considerably darl';(!r than in 

 summer, lieii}g in this rts)M'ct fully equal lo the jirimaries ; and the comparative shades 

 of Ihcir inner and outer webs are exactly as in llie primaries. On tlie crown the white 

 of the foreliead lieeomes obscured and vaiiegated with b]acki,sh or grayish-plumbeons, 

 which glows darker on the na]ie, and on llie sides of the head sends forward a band 

 through tlie eye, to become intensified into a blacker spot just anterior to it. The 

 feet are brownihh-hlack, with little or no reddish ; the bill pure black. The rhaehides 

 of the primal lis are darker than in summer. There is no appreciable difference in the 

 eniarginalion of the tail, nor in the 8hai)e of its individual leathers. 



Wliile chuvymg, w Jiigimt. iliiriiig tli: invvU, the adults are in a peculiar state of 

 •plnimige. The entire under parts (except the inferior caudal teetriees), and the head 

 and sicik all round, are remarlably variegated with pure white and pure black. The 

 relative amounts of the two colors varies with almost every specimen, depending of 

 coui.se u]ioii the particular stage arrived at. In general, the foichead and throat, as 

 far as the l)reast, become first pretty nninterrnptedly white. The crown, occiput, and 

 nape are then ei|ually vaii<'gafed with the two colors, in small spots and lines ; but the 

 auriculars, and a .spot just liefcjre the eye, ale usually pretty purely black. The should- 

 eiK ar>d I'dges of the wings show traces of the giayish-black that is to ajijiear. The 

 ]]ow old and worn-out primaries have lost most of their silvery hoarincss, and the 

 shafts are nearly jiure yellowish-white, except at their extreme apices. The bird in 

 other respects is generally as in summer. 



yoiiinj-iif-llie-iiciir in August. — The size is less than that of the adults; the hill is 

 smaller, weaker, .softer, without very sharply defined angles or ridges. The em.argina- 

 tiou of llie tail is very slight, being only about half an inch, and the lateral Kjctricea 

 want iven the slight elongatiiui and tap(iing which those! of the adults have, being 

 broad lo their very apices, whieh are somewhat oblique truncated. There is an inde- 

 eerilial)le softiiess and gen(;ral mollipilose conditicui to the plumage, readily recogniz- 

 able, both by sight and touch, to the exjiert in such matters. 



Bill brownish-black, tla; base of the lower mandible dull, dirty flesh-color, the 

 inside of the month yellow. Legs and feet light brown. I'Virehead grayish-white, 

 this color extending over the eyes as such, but deepening on the crown and occiput 

 into grayish-brown. This color extends over the nape down to the biick, and there 

 obscures the general idumheous hue of the parts. On the middle of the back, between 

 the slionhh^rs, this brown is quite uuiform; on other parts it meiely forms tips and 

 margins for the feathers, including the sujierior alar and caudal teetriees, and the ter- 

 tials and seajiulars. The row of le.ast upper wing-coverts is grayish-black, as in the 

 adults in winter. The tertials have also whitish tips, in addition to their subtermin.al 

 blown ones. lii'forc thi' eye is a crescent of deep, pure black; behind the eye a patch 

 of jiure black extends over the anriculars and a little distance on the sides of the neck. 

 The under parts are pure white; on each side of the breast there is a large spot of 

 pliimbeocB-brown, which, howevr, does not meet its fellow of the opposite side. The 

 sides under the wings are very light plumbeous, mnch the same hue as the inferior alar 

 teetiires and axillary leathers. The teeondaries are like those of the adults in winter; 

 the, primal ies like those of the full-pluDiaged summer birds, oi ly that their shafts arc 

 HU|ieri(n-ly brown, not white. 



Diwdinioiih of the adult. — Bill above, 1.10; along commissure, l.flO; from feathers on 

 side of lower mandible, l.OfJ ; gonys, O.fiO; height at base, O.-i.''. ; length, 9.25; extent 

 of wings, 24 to 2.'»; wing from cai'iius, ft.'25; tail, :i.7.5; depti of forking, (i.'.Hl; tarsus, 

 0.68; middle toe and claw, O.'JO ; tibias bare, 0.40. 



Dimeyisiotis of the yoiivg-of-Uic-ycar. — Bill above, 0.95 to 1 ; depth at base, 0.20; from 

 feathers on side of lower mandible, 0.'J.'>; gcjuys, 45; tarsus, n,«i() ; middle toe and claw, 

 O.^r.'i; length, 7.7.") to 8; extc'nt of wings, Sti.CO to24 ; tail, 3; depth of emargi nation, C.oO. 

 Ayiuloiiiical cJiaraclem. — The mouth is narrow, its sides concave, and its tip att<'iiii- 

 ated, beyond that of any other species. The palate is soft and vascular to within half 

 an inch of the tip. The median palatal ridge commences far forward; it is narrow, 

 but prominent, its iedges posteriorly, and the edges of the nasal aperture, slightly papil- 

 late. The- sulcus between it and the lateral ridge is well marked and deep. The lateral 

 ridges au! short and sinuate, extending no further back than the median. The poste- 

 rior vaulted space small but well arched, the nasal slit extending far into it. Posteiior 

 fringe of oblique i)apilla; well developed. Tongue exceedingly acute, narrow, longi- 

 tudinally grooved along the dorsum, anteriorly corneous, its apex bilid, its posterior 



