LARIFORMES. 
coloration, and as there are structural features approaching the Noddies while 
the juvenile-plumage is quite unlike that of other Terns, the recognition of 
Onychoprion as a genus is necessary. By the use of this we fix the essential 
nature of this group, and the great difference between this bird and (say) Sterna 
hirundo Linne is not overlooked, as it may be by the use of the generic Sterna 
to cover all Terns. This practice is inferentially recognised by the admission 
that Hydrochelidon is “ a very natural genus ” : the members are Marsh-Terns 
with short tails, distinct coloration, and incised webs. The natural result of 
the examination of many Terns, is acceptance of groups of species which may 
be termed “ natural genera ” or artificial groupings, according to the point of 
view of the individual systematist, but which undoubtedly are aids to the 
student and appear to be based upon reasonable characters. 
VOL. ri. 
309 
