36C Synopsis of the Birds 



Thalassidroma, Vigors. Hydrobates, Boie. 



Petrel-Hirondelle, Temm. 



Bill shorter than the head, slender, feeble, attenuated, ex- 

 tremely compressed, hooked at the point, acute ; edges sharp, 

 greatly approximated ; upper mandible slightly seamed 

 each side : lower shorter, hardly angular beneath, more or 

 less curved and acute at tip, end hardly distinct : nostrils 

 contained in a single tube on the top of the bill : tongue 

 moderate, depressed, entire, slender, acuminate, acute. Head 

 small, rounded above ; eyes large ; neck short : body slender. 

 Feet long, slender ; naked space of the tibia extensive; tarsus 

 longer than the middle toe, slender, perfectly smooth ; toes 

 rather short, slender ; middle toe subequal to the outer ; 

 inner shortest ; the lateral margined exteriorly by a narrow 

 membrane ; webs small, somewhat indented ; hind toe merely 

 a slender, acute nail : nails small, rounded above, in one 

 species quite flat and laminar, but generally curved, com- 

 pressed, and acute. Wings long, acuminate ; first primary 

 shorter than the third ;* second longest. Tail emarginate, 

 or slightly forked, of twelve feathers. 



Female similar to the male. Young hardly differing from 

 the adult. Moult twice a year without changing their colors. 

 Colors black, widi more or less of white, especially on the 

 rump. Species very small : the smallest of web-footed birds. 



Semi-nocturnal : wandering. Seen all over the ocean at 

 wonderful distances from land, principally at twilight, or 

 in stormy weather ; hiding from the sun in clefts of rocks, or 

 in the burrows of quadrupeds. Feed on small marine ani- 

 mals and seeds of sea-weeds ; very fond of greasy substan- 



* The character assigned by Mr. Vigors, of the first primary being 

 longer than the fourth, though perfectly correct as to P. pelagica, cannot 

 stand as generic, since in P. Leachii, it is shorter. We have not been 

 able to verify the character on P. Wilsonii, the specimens we examined for 

 that purpose being in moult. 



