BIRDS — LARINAE — LAliUS. 841 



Eight well marked genera, however, included in this eub-family, are found in the United 

 States. 



1. Larcs. — Of large and medium size ; bill strong and hooked at tip ; mantle generally 

 light colored ; head white ; tail nearly even. 



2. Blasii'ils. — Of middle size ; bill long and rather slender ; head white ; rest of plumage 

 dark ; tail slightly emarginate. 



3. CiiROicocEPHALUS. — Size medium and rather small ; bill moderate or slender ; the head 

 enveloped in summer with a dark colored hood ; tail generally even. 



4. RissA. — Medium size ; bill long and rather strong ; colors light ; hind toe short or 

 rudimenial ; tail even. 



5. Pacopoila. — Of middle size ; bill short and very strong ; mantle light; tarsi rather short ; 

 webs indented. 



6. RHODOSTETniA. — Small in size ; bill short and rather slender ; mantle pale ; neck encircled 

 with a black collar ; tail uniform. 



7. Creagrtjs. — Medium size ; bill very strong and much curved ; mantle grayish white ; 

 tail deeply forked. 



8. XE.^fA. — Of small size ; bill short and rather slender ; mantle bluish gray ; tail moderate 

 and forked. 



LAlRUS, Linnaeus. 



Larus, Likn. Syst. Nat. 1735. 



Ch. — Bill strong and laterally compressed ; the culmen straiglit at the base and curved at the end ; nostrils lateral and 

 linear, placed near the centre of the bill ; wings pointed ; first quill longest ; tail even ; tarsi nearly the length of the middle 

 toe ; feet with a full web ; hind toe elevated. The largest of the family are found m this genus ; none very small. 



There are several well marked groups in this genus, but not sufficiently different for generic 

 distinction. They may be arranged in the following manner : 



A. Leucus, Bp. — Large and powerful in form ; the upper plumage very light in color ; 

 primary quills white, or of the same color as the back. 



Mantle grayish blue ; primaries white at the end for a considerable space L. glaucus. 



Mantle greyish blue ; primaries of the same color as the back, except the tips, which 



are white L. glaucescens. 



]\Iantle pale grayish blue ; primaries of the same color at the base, terminating largely 



with white , L. leucopterus. 



Mantle grayish blue ; primaries ash gray ; the tips marked with a rounded white 



spot L. chalcopterus. 



B. DoMiNiCANUS, Bruch. — Large ; the upper plumage dark slate color ; primaries black near 

 the end ; tijjs white L. rnarinus. 



C. Laroides, Brehm. — Large ; the mantle pearl or bluish gray ; primaries marked near the end 

 with a black band ; tips white. 



Mantle pale bluish gray ; primaries black near the end, with the tips white. . . L. argentatvs. 

 Mantle bluish gray ; primaries crossed near the end with black ; tips white. 



L. cali/ornicus. 

 Mantle dark bluish gray ; primaries black near the end, with the tips white. 



L. occidentalis. 



Angnst 23, 1858. 



106 b 



