Devonshire acre,
Somersetshire acre

In Devonshire and Somersetshire, England, a unit of land area, = 4000 square yards, based on a perch of 15 feet.

John Chalmers Morton.
A cyclopedia of agriculture, practical and scientific: in which the theory, the art, and the business of farming are thoroughly and practically treated. Vol 2.
Glasgow: Blackie and Son, 1855.
Page 938.