Nostrils not tubular, lateral, perforate. Bill with continuous
covering, or only broken by a sort of cere, hooked or straight to
the end. Hallux small and elevated, but always present … _Laridæ_.
Nostrils tubular, disjoined and lateral, or oftenest superior and
united in one double-barrelled tube. Covering of bill in several
pieces; bill always hooked. Hallux minute, rudimentary, or absent …
_Procellariidæ_.