LARIDAE AND STERNIDAE. 



1. with very large, and partly smaller, irregularly shaped and 

 unequally distributed spots, or with hieroglyphic-like figures 

 (such as in Alca torda, Uria lomvia, and others); 



2. with an olive yellowish or brownish ground colour, marked 

 with spots of middling size, more particularly at the big end 

 (such as in Charadrius apricorius, Recurvirostra avosctta, and 

 others) ; and 



3. with a yellowish white ground colour, on which chiefly 

 smaller, sharply accentuated, blackish brown spots are fairly 

 evenly distributed (such as in Larus gelastes), 



STERNA FLUVIATILIS NAUMANN AND S. MACRURA NAUMANN. 



Opinions respecting oological points of difference between these two 

 species are far from harmonizing; the views set forth in the literature 

 on the subject, are frequently in direct contradiction to one another. 



It would appear to me that all that can be said, up to the present 

 at any rate, is that macrura-eggs are as a rule slightly smaller, 

 especially narrower, and, as regards the weight of the shell, slightly 

 lighter than those of fliiviatilis, while a greenish ground colour 

 seems to predominate in macrura and ^ yellowish or yellowish brown 

 ground colour in fliiviatilis. 



Hantzsch ') ascertained (in Iceland), in respect of several niacrura- 

 nests, different stages of incubation in the eggs of each nest, which 

 strengthens his opinion that where there is a mutual difference, 

 frequently strikingly great, in the colour and markings of the eggs 

 from one and the same nest, these eggs have been laid by different 

 female birds. 



') Beitrag ziir Kenntnis der Vogelwelt Islands (Berlin, 1905), p. 146. 



