Note:  Do not rely on this information. It is very old.


Theca, a genus of fossils ranging from the Cambrian to the Permian periods, but most characteristic of the former; it is of interest as it is one of the best known of the group regarded as Palaeozoic Pteropoda (q.v.). It is, however, very doubtful whether it really belongs to that order while its correct name is Hyolithes.