PETRELS. 
529 
Allied Petrels The small wedge-tailed petrel ( Halocypetna microsoma), 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. hornbyi), 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 
