Spirolina, [349].

Spirulirostra Bellardii, [463].

Spondylus spinosus, [399].

Sponges, characters of, [220].

-------, arrangement of recent, [221].

------- in chalk and flint, [222].

Spongilla, [221].

Spongites clavellatus, [224].

--------- flexuosus, [226], [213].

--------- labyrinthicus, [225], [243].