552 ORNITHOLOGY AND OOLOGY. 



SUB-ORDER GAVI^. 



Family PROCELLARID^. The Petrels. 



Bill more or less lengthened, compressed, and deeply grooved, appearing to be 

 formed of several distinct parts; the tip is strong, much hooked, and acute; the nos- 

 trils open from distinct tubes, either single or double, and are situated at the base of 

 the upper mandible. 



All the birds embraced in this family are strictly oceanic, some of the smaller 

 species only being observed in bays near the ocean during or after a storm. They 

 vary greatly in size, some being quite diminutive, while others are equal in dimen- 

 sions to the largest known birds of flight. 



Two sub-families, namely, Dlomedeince and Procellarince, constitute this family, 

 the distinguishing characters of which are as follows : — 



DiOMEDEiN.E. — Bill very strong, curved, and acute at the end; nostrils short, 

 tubular, and situated on the sides of the upper mandible near the base. 



Procellarince. — Bill more or less strong, curved at the end, and pointed; 

 nostrils tubular, situated on the culmen, near the base, and opening forwards. 



Sub-Family Procellarin^. The True Petrels. 



The bill more or less strong, compressed, tip much hooked and pointed ; the nos- 

 trils tubular, to a greater or less extent, and situated on the basal part of the culmen; 

 generally of medium or small size, wandering in their habits, and capable of sus- 

 taining themselves on wing for a great length of time. 



THALASSIDROMA, Vigors. 



Thalassidroma, Yi^ors, Zool. Jour. (1825). 



Bill shorter than the head, slender and weak, the tip curved and acute, the sides 

 compressed and moderately grooved; nostrils at the base of the culmen tubular 

 and prominent; wings long and narrow, the second quill longest; tail forked or 

 emarginate; legs slender and very long; tibia bare for a considerable space; ante- 

 rior toes rather short and slender, united by an indented web ; a short spur in place 

 of the hind toe. 



THALASSIDROMA LEACHII. — Bonaparte. 



Leach's Petrel. 



Procellaria Leackii, Temm. ISIan., II. (1820) 812. 



Tlialassidrmna Leadiii, Nuttall. Man., II. (1834) 326. Aud. Cm. Biog., III. 

 (1835) 434. lb., Birds Am., VII. (1844) 219. 



1 See Introduction. 



