The group of Membraniporæ, with a small median barred avicularium placed immediately above the oæcium, of which M. Griffithi, Bryd., is a leading instance, contains several Senonian members in addition to the Trimingham forms (M. Triminghamensis, M. anterides, M. humiliata) which I have already described in this Magazine. They seem to arise first in the zone of Micraster cor-anguinum.

Membranipora Simulacrum, sp. nov. (Pl. XXVI, Figs. 1, 2.)

Zoarium unilaminate, always adherent.

Zoæcia large, very slightly subpyriform, areas oval, with average length .5 to .55 mm. and breadth .3 mm.; side walls bent slightly inwards, and so low and slender that at a hasty inspection they might be taken to be mere ghosts of some species with a low arched front wall.