BLACK-THROATED DIVER. 347 
is about a third of the whole length distant from the extremity. Their 
form is that of the Red-throated Diver, which however they exceed 
in size. he shell is rather thick, the surface roughish, the ground 
colour chocolate tinged with olive, sparingly spotted at the larger end 
with very dark umber and black, and sprinkled all over with very small 
dots of the same colour. 
I have represented an adult male, a female, and a young bird. 
CotymsBus arcticus, Linn. Syst. Nat. vol. i. p. 221.—Lath. Ind. Ornith. vol. ii. 
p- 800.—Ch. Bonaparte, Synopsis of Birds of United States, p. 420. 
Cotymesus arcricus, BLack-THROATED Diver, Richards. and Swains. Fauna Bore- 
ali- Americana, vol. ii. p. 475. 
BLack-THROATED Diver, Nuttall, Manual, vol. ii. 
Adult Male. Plate CCCXLVI. Fig. 1. 
Bill as long as the head, straight, stout, higher than broad at the 
base, much compressed toward the end, and tapering to a point. Up- 
per mandible with the dorsal line descending and considerably convex 
toward the end, the ridge convex, narrowed toward the point, the sides 
convex beyond the nostrils, the edges involute for half their length in 
the middle, direct at the base and toward the end, the tip narrow and 
sharpish. Nasal groove rather long and narrowed; nostrils sub-basal, 
linear, direct, pervious. Lower mandible with the angle extremely 
narrow, and very long, the dorsal line ascending and very slightly con- 
vex, the ridge convex and narrow, the edges sharp and involute, the 
tip attenuated. 
Head of moderate size, oblong, narrowed before. Neck rather long 
and thick. Eyes of moderate size. Body elongated, much depressed, 
of an elliptical form viewed from above. Wings small. Feet short, 
rather large, placed very far back; tibia almost entirely concealed ; 
tarsus short, exceedingly compressed, sharp-edged before and behind, 
covered all over with reticulated angular scales, hind toe extremely 
small, externally marginate, connected with the second for half its length 
by a membrane, which extends, narrowing, to the end; the anterior toes 
connected by articulated membranes, the fourth or outer longest, the 
third a little shorter, the second considerably shorter than the third ; 
all covered above with numerous narrow scutella ; the second toe with 
a free two-lobed membrane, the claws very small, depressed, blunt. 
