4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 98 



can see. While at first glance they appear smaller than nesiotes, with 

 the considerable series I have seen this is not indicated in actual 

 measurement. Following is a summary of the dimensions of the 

 available specimens from Isabel Island and the Tres Marias : 



Males (9 specimens), wing 366-389 (375), tail 161 -193 (183), 

 culmen from base 85.6-92 (89.4), depth of bill at gonydeal angle 

 n.i-12.2 (11.5), tarsus 43.5-48.5 (46.3), middle toe with claw 69-76.7 

 (72.7) mm. 



Females (8 specimens), wing 391-418 (403), tail 178-198 (185), 

 culmen from base 92.8-100 (95.3), depth of bill at gonydeal angle 

 11.9-14 (12.9), tarsus 45.0-53.5 (48.8), middle toe with claw 72.9- 

 83.8 (78.6) mm. 



Comparing these figures with those based on the birds from 

 Clipperton we find that the wing lengths are almost identical. In 

 length of culmen the smallest birds come from the supposed "albiceps" 

 group, the average difference in length of culmen amounting to 

 about 4 percent, but there is definite overlap in individuals. The bill 

 also is very slightly more slender, though here again there is individual 

 variation. The length of the tarsus in the two is quite similar, though 

 the Isabel-Tres Marias specimens seem to have slightly smaller feet 

 as indicated by the length of the middle toe with claw. On the basis of 

 the material seen it appears to me that the differences presented are 

 slight and do not permit recognition of albiceps as distinct from 

 ncsiutes at present, especially in view of the large size of the birds 

 concerned, a conclusion reached only after somewhat prolonged con- 

 sideration. Possibly more material may bring out the size distinction 

 clearly, but from what I have seen I should expect instead that it 

 might nearly or entirely disappear. It is only fair, however, to add 

 that Mr. van Rossem has examined the National Museum material 

 with me and does not agree. 



Sula leucogaster etesiaca Thayer and Bangs : 



Sula etesiaca Thayer and Bangs, Bull. Mus. Comp. Zool., vol. 46, June 1905, 

 p. 92 (Gorgona Island, Colombia). 



Similar to brewsteri but darker ; male with light color of head as in 

 brewsteri but apparently less extensive in the fully adult bird ; female 

 closely similar to plot us but slightly darker and more uniform in shade 

 of brown. 



Range.— -Cocos Island, Costa Rica, through the Pearl Islands, 

 Panama, to Gorgona Island, Colombia. 



Measurements (in millimeters). — Males (15 specimens), wing 360- 

 384 (370); tail 183-187 (181), culmen from base 82-93.3 (88.6). 



