518 PROCEEDINGS OF THE NATIONAL HIV8EVM. vol.40. 



c^. Size smaller (wing averaging less than 350 mm.). 



b^. Upper parts very dark gray Thalasseus bergii cristatiLS (p. 520). 



6^. Upper parts medium or light gray, 

 c^ Mantle darker. 

 d}. Smaller (wing averaging less than 325 mm.). 



Thalasseus bergii halodramus (p. 522). 

 <P. Larger (wing averaging more than 325 mm.). 



e'. Darker above, and smaller Thalasseus bergii poliocercus (p. 525). 



c^. Paler above, and larger Thalasseus bergii pelecanoides (p. 523). 



c*. Mantle paler. 



dK Larger and darker Thalasseus bergii rectirostris (p. 524), 



d^. Smaller and lighter Thalasseus bergii thalassinus (p. 519). 



THALASSEUS BERGII BERGII (Lichtenstein). 



Sterna bergii Lichtenstein, Verz. Doubl. Zool. Mus. Berlin, 1823, p. 80 (Cape of 



Good Hope, southern Africa). 

 Sterna longirostris Lesson, Traits d'Om., 1831, p. 621 (no locality; type-locality 



designated as Cape of Good Hope by Stresemann, Novit. Zool., vol. 21, 



February 25, 1914, p. 57). 



Suhspecific characters. — Of large size and pale coloration. 



Measurements. — Wing, 340-372 (average, 351.4) mm.; tail, 175- 

 193 (182.4); exposed culmen, 58-68 (62.2); tarsus, 29-33 (31.6).^ 

 Wing, 360-370 (364.3). ^ 



GeograpTiical distribution. — Coasts of southern Africa, north, on the 

 western side to Walfisch Bay, German Southwest Africa, and on the 

 eastern coast to Zanzibar, off German East Africa; and Madagascar. 



As with aU the races of this species, there is considerable individual 

 variation in the gray of the upper surface, but while some darker 

 birds occur, the average is considerably lighter than in any of the 

 other large subspecies. This form is also larger than any other 

 excepting Thalasseus hergii velox and Thalasseus bergii bakeri. 



Detailed measurements of the specimens of the present race ex- 

 amined are as follows : 



Measurements of specimens of Thalasseus bergii bergii. 



' Five specimens, from southern Africa. 

 2 Four specimens, measured by Stresemann. 

 « Used in measurement averages on p. 518. 



