Ridges and Valleys
When more than one corallite is located in a depression on the colony surface, we say that the corallites are located in valleys. The thin, high sections of colony surface separating the valleys are called ridges. The genus Oulophyllia (p. 9 of the Coral Finder) has distinct ridges and valleys.
Corallites may form distinct individuals with clear walls, but in some genera, they cluster in valleys separated by ridges of skeleton. It is important to be aware the valleys and ridges can differ in width, depth, length and sharpness. For example, the valleys of Leptoria (p. 8 of the Coral Finder) are long, thin and separated by zipper-like ridges. Whereas the corallites of Pavona (p.7 of the Coral Finder) may group in short valleys with fine sharp ridges.
Note: the terms wall and ridge are often used interchangeably when describing meandering colonies. There is a very important distinction to understand with respect to ridges. Typically the term wall, as in corallite wall, implies a structural role in the formation of the corallite and is important to the definition of many coral genera. e.g. the corallites of the genus Favia has separate corallite walls whereas the genus Favites have common corallite walls. But in some genera ridges of skeleton can be found on the colony surface independent of corallite formation.