A new species of an ascidian, Pycnoclavella stanleyi, is described. It occurs in some abundance near low tide level at Pacific Grove, Calif. It differs from P. aurilucens Garstang, known only from the western end of the English Channel, mainly in the character of the colony rather than that of the individual zooid or tadpole larva. Colonies are flat, incrusting, heavily impregnated with sand, have a gelatinous matrix, and exhibit some orange pigmentation. Colonies of P. aurilucens are without sand, have a leathery texture, are green, and are not intertidal. Both species have zooids with seven rows of gill slits on each side, a posterior vascular budding stolon as in Clavelina, and a tadpole larva with an ocellus but not an otolith.