DIELASMA

genus of extinct brachiopods, or lamp shells, that occur as fossils in rocks deposited in marine environments of Carboniferous to Permian age (between 360 and 245 million years old). The two small, rather smooth valves of the shell of Dielasma are slightly convex in profile, but the pedicle, or foot, valve is much larger than the brachial, or upper, valve. Growth lines are generally apparent. In some respects Dielasma is similar to Composita, a brachiopod with similar time range and habitat.