LARID] LABUS 



Key of the Genera. 



A. Bill without a horny cere. 



a. Bill long, straight and rather slender, both 



mandibles approximately equal. 

 a'. Tail short and nearly square; webs between 



the toes emarginate Hydrochelidon, p. 4'29. 



/;'. Tail distinctly forked, outer feathers more 

 or less elongate and pointed ; toes fully 



webbed Sterna, p. 433. 



t- 1 . Tail graduated, the outer pair of tail-feathers 



distinctly shorter than the next pair. 

 a'-. Bill strong and decurved ; fourth pair of 



rectrices the longest Anous, p. 445. 



b~. Bill slender and long ; third pair of rec- 

 trices the longest Micranous, p. 446. 



c-. Bill stout at the base, culmen straight or 

 upcurved ; second pair of rectrices the 

 longest Gygis, p. 447. 



b. Bill with both mandibles much compressed, 



the lower exceeding the upper in length BhyncJiops, p. 448. 



c. Bill stout, not exceeding the head in length; 



upper mandible somewhat longer than the 

 lower, tip hooked and bent down over .that of 

 the lower Larus, p. 422. 



B. Bill with a horny cere overhanging and partially 



concealing the nostrils Htcrcorariu-s, p. 451. 



Family I. LABIDJE. 



Sternum with two notches on each side posteriorly; femoxo- 

 caudal, accessory femorocaudal, accessory semitendinosus and 

 ambiens muscles all present ; caeca small and rudimentary. 



The external characteristics are given in the description of the 

 single genus Larus represented in our fauna. 



Genus I. LARUS. 



Type. 

 Larus, Linn. Syst. Nat. 12th ed. i, p. 224 (1766) L. marinus. 



Bill stout and hooked, the upper mandible slightly longer than 

 the lower one and bent down over its tip ; bill shorter than the head 

 and about three times as long as deep ; no cere at the base of the 

 bill ; nostrils linear ovals about half way down the bill ; wings 



