The 
Procellariidae family are a group of 
seabirds in the 
bird order 
Procellariiformes, which also includes  the 
Albatross family, 
Diomedeidae, the  
storm-petrels, 
Hydrobatidae, and the 
diving petrels, 
Pelacanoididae. 
The family Procellariidae is the main radiation of medium-sized 'true petrels', characterised by united nostrils with medium septum, and a long outer functional primary. It is dominant in the Southern Oceans, but not so in the Northern Hemisphere. 
It includes:
- The fulmar group
 - The prions, genus Pachyptila. A specialised group of six very numerous species, all southern. They have a small, fulmar-like form and filter-feed on zooplankton.
 - The gadfly petrels. These are large and agile short-billed petrels in the genus Pterodroma.
 - Shearwaters in the genera Calonectris, Puffinus and  Procellaria. The three species in the last genus are named as petrels
 - Petrels of indeterminate relationships
 
 
All Wikipedia text 
is available under the 
terms of the GNU Free Documentation License