Inverted cone sections rising from a column with ribs making blind tracery that fan out to form the vault or ceiling.
For more details see the longer article prepared for the Cathedral section of CHAS Notebook.
Local examples (click to enlarge)
Bell Harry tower, cathedral
Edward the Confessor chapel , cathedral
Deans' chapel, cathedral
South-west (Chichele) tower, cathedral
For help with terminology applied to the various types of rib. click here