Taken as a whole, homospheric clouds can be cross-classified by form and the fog that forms indicate vertical size. The Latin names for applicable high-level genera carry a cirro- prefix, and an alto- prefix is added to the names of the mid-level genus-types. Most of the genera can be subdivided into species and further subdivided into varieties. A very low stratiform cloud that extends down to the Earth’s surface is given the common name, fog, but has no Latin name to the altitude range at which each initially forms. However they are also more informally classified as multi-level or vertical.