222 
Genus VI.— PEA.ETON, Linn. 
TROPIC BIRD. 
Bill as long as the head, stout, very much compressed, slightly curved, 
tapering, acute, opening to beneath the eye ; upper mandible with the 
dorsal line slightly arched, the ridge narrow, rounded, the sides sloping 
and slightly convex at the base, nearly erect towards the end, the edges 
sharp, direct, irregularly broken, the tip acuminate ; nasal groove short, 
near the ridge ; lower mandible with the angle long, and extremely narrow, 
the dorsal line straight and ascending, the sides erect and slightly convex, 
the tip acuminate. Nostrils basal, linear, very small. Head rather large, 
ovate ; neck short and thick ; body rather full. Feet very short ; tibia bare 
for a considerable space ; tarsus extremely short, roundish, covered with 
small round scales ; toes rather small, placed in the same plane, and con- 
nected by reticulated webs ; first very small, third a little longer than 
fourth, all scutellate above. Claws small, arched, compressed, rather sharp, 
that of the third toe with a thin entire inner edge. Plumage soft, blended, 
on the back rather compact. Wings long, acute, the first quill longest. 
Tail of twelve feathers, tapering, the two middle feathers extremely 
elongated, narrow, and tapering. This genus appears to be intermediate 
between Sula and Sterna. 
