Corolla with a spur: in some species the corolla has an obvious outgrowth which serves as a collector of nectar, called spur:

Examples are the flowers of Delphinium...:

...those of the genus Aquilegia..:

...the flowers of several orchids..:

...those of violets...

...and those of several other species of herbaceous plants.

In some cases the 'spur' is very short and sac-like, e.g. in the genus Fumaria: