644 STERNA ARCTICA. 



Feet very small ; tibia bare to a considerable extent ; tarsus 

 extremely short, roundish, covered anteriorly with small 

 scutella, elsewhere with roundish scales. Hind toe extremely 

 small, the rest slender, the third longest, the fourth not 

 much shorter, the membranes with a concave margin. Claws 

 rather long, arcuate, compressed, acute, that of the middle 

 toe very much larger, and having the inner edge dilated. 



Plumage close, blended, soft ; the feathers broad and 

 rounded. Wings very long, narrow, pointed ; primary quills 

 very narrow, tapering, somewhat incurvate, the first longest ; 

 secondaries short, broad, incurved, rounded. Tail long, very 

 deeply forked, the lateral feathers attenuated so as to become 

 nearly filiform, the medial feathers shortish and broadly 

 rounded ; the fork rounded. Wings to half an inch of the 

 end of the tail. 



Bill carmine, inclining to vermilion. Iris broAvn ; edge 

 of eyelids black. Feet deep rich crimson; claws bluish- 

 black. Head above and upper part of hind-neck deep 

 black, tinged with green. The general colour of the plu- 

 mage, on the lower as well as the upper parts, is pale bluish- 

 grey ; the upper and lower tail-coverts, the tips of the 

 secondary quills, and the under surface of the wings white. 

 Outer web of first quill black, grey toward the tip, part of 

 inner web along the shaft, outer web and part of inner of 

 all the primaries bluish-grey ; outer w^eb of outer tail-feathers 

 bluish-grey, the rest white. 



Length from end of tail 15 j inches ; extent of wings 31 ; 

 wing from flexure lO-i- ; tail 7^ ; bill along the ridge H, along 

 the edge of lower mandible 1\^ ; tarsus -/^ ; middle toe and 

 claw 1. Another individual : — Length 15^ inches ; extent of 

 wings 29^ ; bill 1-fV ; tarsus -j-^^ ; middle toe i^. Both fi-om 

 the Bass Rock, June, 1824. 



Female. — The bill and tail-feathers somewhat shorter ; 

 otherwise no external difference is observable. 



Length to end of tail 15 inches ; extent of wings 30. 



Vakiations. — Slight differences are observed in the tint 

 of the plumage, especially that of the breast, which is some- 



