II. Colymbidae

Bill slightly compressed, smooth, not covered by a membranous skin; the tomia simple, or only slightly denticulated: wings short: legs placed at the extremity of the body: tarsi very much compressed: feet four-toed, pal-mated, or fssopalmated: hind toe free.

100. Podiceps

Bill moderate, straight, robust, forming a lengthened cone, sharp-pointed; upper mandible slightly inclining at the tip; lower mandible with the gonys ascending: feet short; anterior toes fissopalmated; hind toe lobated: claws broad, and much depressed: wings with the three first quills nearly equal, and longest: tail wanting.

101. Colymbus

Bill rather longer than the head, straight, robust, nearly cylindrical, sharp-pointed; the tomia of both mandibles inflected; gonys ascending: feet short; anterior toes long, entirely palmated; hind toe short, and lobated: claws depressed: wings with the first or second quill longest: tail very short, rounded.

III. Alcidae

Bill very much compressed, often transversely grooved at the sides: wings short, sometimes wholly unfit for flight: legs placed at the extremity of the body: feet three-toed, entirely palmated.

102. Uria

Bill moderate, strong, straight, convex above, much compressed at the sides, sharp-pointed; upper mandible slightly deflected at the tip; gonys of the lower mandible ascending; tomia curving inwards from the base to the middle: nostrils basal, lateral, pervious, elliptic-linear, half concealed by a plumose membrane: tarsi very much compressed: wings very short; first quill longest: tail short, of twelve feathers.

103. Mergulus

Bill shorter than the head, rather thick, convex, conical, slightly curved, covered at the base with downy feathers; both mandibles notched at the tip: nostrils basal, lateral, round, partly concealed by a plumose membrane: wings not reaching to the tail; first and second quills equal, and longest: tail short, of twelve feathers.

104. Fratercula

Bill shorter than the head, thick at the base, very much compressed anteriorly, higher than long, the culmen more elevated than the crown of the head; both mandibles arched, transversely furrowed, and notched at the tip: nostrils basal, marginal, oblong-linear, almost entirely closed by a large naked membrane: wings short, narrow, and acuminated; first and second quills equal, and longest: tail short, of sixteen feathers.

105. Alca

Bill a little shorter than the head, rather longer than high, much compressed, cultrated; both mandibles laterally sulcated; upper one hooked at the extremity; lower one with the gonys ascending, the mental angle prominent and rounded: nostrils marginal, nearly concealed by the advancing fronfal feathers: wings short, and narrow: tail short, of twelve to sixteen feathers.

IV. Pelecanidae

Bill strong, sometimes compressed; the tomia denticulated: wings long, and powerful: legs very short, in or near the equilibrium: feet with four toes, all united by one continuous membrane.

106. Phalacrocorax

Bill a little longer than the head, straight, compressed, culmen rounded; upper mandible with a longitudinal furrow on each side, the dertrum distinct and strongly hooked; lower one with the tip truncated: nostrils concealed: face and throat naked: tibiae feathered: middle claw with the inner margin denticulated: wings moderate; first quill shorter than the second, which is longest: tail rounded.

107. Sula

Bill a little longer than the head, robust, straight, large at the base, compressed and attenuated towards the tip; culmen rounded; upper mandible laterally sulcated, the tip slightly hooked: gape extending beyond the eyes: face naked: nostrils concealed: tibiae naked at bottom: middle claw with the inner margin denticulated: wings long, and acuminated; first quill longest, or equal to the second: tail graduated.

V. Laridae

Bill without denticulations: icings very long: legs in or near the equilibrium: aves. 77 three anterior toes united; hind toe free, sometimes represented by a simple nail, or altogether wanting.

108. Sterna

Bill as long as, or a little longer than the head, nearly straight, rather compressed, slender, attenuated towards the tip, sharp-pointed; mandibles of equal length, the upper one slightly bending at the tip, lower one with the mental angle a little projecting: nostrils longitudinal, oblong-linear, pervious: feet weak, small, four-toed; membranes deeply notched: wings long, acuminated; first quill longest: tail generally forked.

(1. Sterna). Wings very long: tail deeply forked. (2. Anous). Wings moderate: tail even.

109. Larus

Bill moderate, strong, cultrated, much compressed; the .culmen continuous, bending downwards at the tip; gonys obliquely ascending, straight; mental angle strongly projecting; tomia sharp: nostrils longitudinal, medial, oblong-linear, pervious: legs moderate: anterior toes with the membranes entire; hind toe small, high on the tarsus, rarely wanting: wings long; first or second quill longest: tail generally even.

(1. Xema). Tail slightly forked. (2. Larus). Tail even.

110. Lestris

Bill moderate, strong, thick, rounded above, compressed towards the tip; culmen and dertrum distinct, the latter convex and strongly hooked; gonys straight, obliquely ascending; mental angle projecting: nostrils immediately behind the dertrum, diagonal, narrow, closed behind, pervious: hind toe very small, nearly on a level with the others: wings with the first quill longest: two middle tail feathers elongated.

111. Procellaria

Bill more or less elongated, straight, subcylindrical, depressed and dilated at the base; culmen and dertrum distinct; the latter convex, much compressed, and strongly hooked; lower mandible with a longitudinal furrow on each side: gonys concave, more or less ascending: nostrils at the extremity of an open truncated tube extending along the culmen: a simple claw in the place of a hind toe: wings long; first or second quill longest.

(1. Procellaria). Bill moderate, robust; lower mandible straight, somewhat truncated at the tip; mental angle projecting: nostrils opening by a single orifice, the tube extending half the length of the bill: tail slightly rounded.

(2. Puffinus). Bill longer than the head, slender; lower mandible pointed, deflected at the tip, following the curvature of the upper; mental angle obsolete: nostrils in a double tube extending one-fourth of the length of the bill: tarsi moderate: tail rounded.

(3. Thalassidroma). Bill shorter than the head, slender; lower mandible pointed, deflected at the tip, following the curvature of the upper: mental angle obsolete: nostrils opening by a single orifice, the tube extending half the length of the bill: tarsi slender, elevated: tail square, or slightly forked.