The simplest form, known as the waggon or barrel vault, is a semicircular arch spanning two walls, whilst a more elaborate contrivance consists of two intersecting vaults of the same height crossing each other at right angles, which was used in Rome as early as 75 B.C. These two forms were sometimes supplemented by what are distinguished as conches or half-domes over external semicircular recesses, of which the apse is a characteristic example.
"Architecture"
Nancy R E Meugens Bell
Then they banged the temple bells and blew the conches louder than ever.
"The Jungle Book"
Rudyard Kipling
Tirant immediately had large basins filled with water, as well as conches, casks and tubs, and all the friars and clerics came, for Tirant had had many monasteries and even more churches built in the cities he had taken, and many clerics and friars had come from the Christian realms.
"The White Knight: Tirant lo Blanc"
Joanot Martorell and Marti Johan d'Galba