A form of rib vaulting. Here, additional ribs (tiercerons, from tierce, third) spring from the pillars
at the corner of each bay to the ridge ribs along the top of the vault or to lateral ribs. A later version, where additional ribs did not spring from pillars ('springing points') but joined up other bosses, was known as lierne vaulting. Where liernes grew more numerous, and created 'star' patterns, the result was known as stellar vaults.
Local examples (click to enlarge)
All Saints' chapel in the cathedral – accessible to the public on Open Days only
For help with terminology applied to the various types of rib, click here