PETRELS. 529 



The small wedge-tailed petrel {Halocypetna microsotna), of the 

 coast of Lower California, is the sole representative of a genus 

 distinguished from the above by the tail being much rounded, the metatarsus 

 exceeding the length of the third toe, and by the absence of any white on the rump. 

 Leach's petrel {Cymochorhea leucorrhoa) belongs to an allied genus, comprising 

 several somewhat larger species readily characterised by the deeply forked tail, 



STORM-PETRELS ON THE WAVES (^ nat. size). 



in which the feathers have very broad tips, while there may or may not be a white 

 rump-patch. The species named has a very wide distribution, being common to 

 both the Atlantic and Pacific. A fourth genus, represented by the fork -tailed 

 petrel (Oceanodroma furcata) and Hornby's petrel (0. hornhyi), of the North 

 Pacific, differs by the feathers of the forked tail being scalloped at the end, there 

 being no white patch on the rump, and the plumage being either uniform bluish 

 ashy or grey, with the forehead cheeks, or collar on the throat, and the under-parts 

 white. 



VOL. IV. — 34 



