NO. 2121. RACES OF THALAS8EV8 BERG1I—0BERH0L8ER. 517 



of an author to designate as the type of a polytypic genus, the type of 

 which has remained unfixed, a species which has already become the 

 monotypic type of a genus subsequently instituted. There seems, 

 however, to be little doubt of the wisdom and reasonableness of the 

 affirmative decision in such cases. The nomenclatural situation of 

 the generic group now under our consideration is as follows: Boie 

 was the first author to divide the Linnaean genus Sterna, and he, in 

 1822,^ proposed the generic nameTJialasseus for Sterna caspia Pallas 

 { = Hydroprogne caspia [Pallas]), Sterna cantiaca GmeUn ( = Sterna 

 sandvicensis Latham), and Sterna anglica Montagu ( = Gelochelidon 

 nilotica [Gmelin]). The type of Thalasseus w&s ^ist designated by 

 Wagler in 1832 ^ as Sterna cantiaca Gmelin, which species had, how- 

 ever, meanwhile (in 1829) been made the type bymonotypy of the 

 genus ActocTielidon Kaup.^ The latter generic term must therefore 

 fall as a synonym of Thalasseus Boie; as must of course also the later 

 Pelecanopus Wagler,* the type of which by monotypy is Sterna pele- 

 canoides King {= Thalasseus hergii pelecanoides [King]). As there 

 seem to be no other apphcable names, the proper generic designation 

 of the group comprising Sterna hergii is therefore Thalasseus Boie. 

 The following species, together with their subspecies, belong to this 

 genus : 



Thalasseus hernsteini (Schlegel). 



Thalasseus hergii (Lichtenstein) . 



Thalasseus hengalensis (Lesson) ( = Sterna mccZia Horsfield not 

 Vieillot). 



Thalasseus elegans (Gambel). 



Thalasseus eurygnathus (Saunders). 



Thalasseus maximus (Boddaert). 



Thalasseus sandvicensis (Latham) , 

 The chief differential characters of the recognizable races of 

 Thalasseus hergii appear in the following key: 



KEY TO THE SUBSPECIES OF THALASSEUS BERGn. 



a'. Size larger (wing averaging more than 350 mm.). 

 h^. Upper parts of a much paler gray. 



c*. Lighter above Thalasseus hergii hergii (p. 518). 



(?. Darker above Thalasseus hergii gwendolenae (p. 526). 



6^. Upper parts of a much darker gray. 



c^ Larger (wing averaging about 380 mm.) Thalasseits hergii hakeri (p. 519). 



&. Smaller (wing averaging less than 370 mm.). 

 d}. Lighter and larger (wing averaging about 368 mm.). 



Thalasseus hergii velox (p. 519). 

 d^. Darker and smaller (wing averaging about 357 mm.). 



Thalasseus hergii edwardsi (p. 520). 



1 Isis, 1822, p. 563. 



2 Idem, 1832, p. 1225. 



8 Skiz. Entwickl.-Gesch. Natiirl. Syst. Eur. Thierwelt, 1829, p. 31. 

 « Isis, 1832, p. 277. 



