34 



BULLETIN 3t), UNITxiD STATES NATIONAL MUSEUM. 



The four skulls of known sex in the national collection have the fol- 

 lowing absolute proportions : 



Measurements of four skulls of T. tursio. 



Measurements. 



Totallensth , 



Length of beak 



IJreadth of beak at notches , 



Breadth of bealc at middle 



Breadth of iuteiiuaxillso at middle 



Depth of beak at middle 



Len jith of tooth-lino 



Breadth across orbital processes of 



frontal 



Length of mandible 



Depth at coronoid 



Teeth 



Ago 



Sex 



Condition. 





43.3 



^2.4 



11.2 



7.0 



3.7 



19.4 



20.0 



30.2 



8.1 



(24-2^ 



I 24-24 



Young. 



d ' 

 Fresh. 



^P^ 



43.9 



24.1 



10.1 



6.0 



3.2 



2.7 



20.4 



20.4 



37.5 



8.4 



24-24 



23-23 



Young. 



c? 

 Fresh. 





4t.0 

 24.4 

 10.3 

 6.4 

 3.3 



21.1 



19.3 



37.6 



7.9 



23-23 



23-25 



Young. 



9 

 Fresh. 



W 



52.9 

 28.9 

 12.6 

 8.0 

 4.4 

 2.8 

 24.8 



24.7 



45.0 



9.4 



26-2 5 



24-24 



Old. 



Fresh. 



rroiu these measurements we select the following for comparison 



Measurements. 



Total length 



Length of beak 



Breadth of beak at maxillary notches 

 Breadth of beak at middle 



20901, ,/ a. 

 Fire Island, 

 N. Y. (young). 



Cm. 



4.-5.3 



22.4 



11.2 



7.0 



16504, d b. 



Cherrystone 



Point, V.a. 



(young). 



Cm. 

 43.9 

 24.1 

 10. 1 



e.9 



20902, 9 c, 

 Turkey Gut, 



^^\^ (young). 



Cm. 

 44.0 

 21.4 

 10.3 

 6.4 



22304, $d, 

 Ilatteras, 

 N.C. (old). 



Cm.. 



52.9 



28.9 



12.6 



8 



A comparison of the length of the beak, relative to the total length, 

 and of the width of the beak at its base and at its middle relative to 

 its total length, gives the following results : 



The same diversity appears here as in the previous case. The old 

 female, which would be supposed to have the sexual characters strongly 

 marked, has a relatively shorter and wider beak at the base than one of 

 the young males, but a longer and narrower beak than the other. 



Coming now to the series of twenty-one skulls, before mentioned, we 

 find the same variation. In some the beak is long and narrow, and vice 



