Dictionary:

turtleback

  (tûr'tl-băk')

Something shaped like the back of a turtle, especially:

1. Nautical. An arched structure erected over the deck of a ship as protection from heavy seas.
2. Archaeology. A stone tool with a convex side.

1. See blistering, 1.
2. In plastering, a localized condition of checking, 3.