488 



PKOCELLAEIID^ 



PRION 



with hexagonal scutes ; claw of the hind toe minute ; size small ; 

 plumage slaty-blue. 



This genus, containing the Blue Petrels generally termed 

 " Whale Birds " by Sailors, ranges over the Southern Ocean. Five 

 species, all of which have been reported from the Cape seas, are 

 usually recognised. 



Li b c 



Pig. 151. — Bills of (a) Prion desolatus, (6) Primi banksi, (c) Prion vittahis, 

 rom above, x j 



Key of the Species. 



A. Outer tail-feathers white, the middle ones tipped 



with white P. coenileus, p. 488. 



B. Outer tail-feathers grey, central ones tipped with 



black. 



a. Bill very wide, 0'65 to O'SO at base, edges of 



maxillee convex P. vittatuSj-p. 490. 



b. Bm wide, 0"50 to 0"55, edges of maxillse convex P. banksi, p. 489. 



c. Bill narrow, about 0"40 at base, edges of maxillse 



almost straight P. desolatus, p. 491. 



d. Bill narrow, smaller and more compressed, and 



head paler than in the other species P. brevirostris, p. 492. 



797. Prion cseruleus. Blue Petrel. 



Prooellaria oasrulea, Gmel, Syst. Nat. i, p. 560 (1788) ; Layard, B. S. 

 Afr. p. 361 (1867). 



Prooellaria forsteri. Smith, Illuslr. Zool. S. Afr. Aves, pi. 53 (1840). 



Halobsena cserulea, SJiarpe, ed. Layard's B. S. Afr. p. 768 (1884) ; Swin- 

 burne, Proc. B. Phys. Soc. Edin. ix, p. 198 (1886) ; Salvin, Cat. 

 B. M. XXV, p. 431 (1896) ; Shelley, B. Afr. i, p. 168 (1896). 



Prion cseruleus, Beichenoiu, Vogel Afr. i, p. 31 (1900) ; Vanhoffen, Joi^rn 

 Ornith. 1901, p. 310. 



