Muqarnas
Tiers of small niche-cells corbelled one above another to fill a half-dome.
The rules it illustrates
Muqarnas: a vault of small niches. Fill a half-dome, squinch or cornice with tiers of small concave cells, each tier corbelled forward from the one below and each cell set over the junction of two cells beneath.
Muqarnas are designed in plan. Draw the muqarnas as its plan (the projection of every tier on the floor) and build it up from the plan tier by tier with a fixed height to each tier.
Where it appears in the book
In the styles Moorish (Western Islamic), Persian Islamic (Seljuk, Timurid and Safavid).
In the chapters The Islamic World.