The species of Polyzoa here described, and most of which appear to be new, occurred on shells from Mazatlan, on the Gulf of California; and for the opportunity of examining them, I have been indebted to the kindness of Mr. Phillip Carpenter, who has prepared a descriptive catalogue of the “Mazatlan Mollusca,” for the British Museum. The typical specimens of the forms here noticed, will be found in that Institution.

Order. Polyzoa Infundibulata.

Sub-order I. Cheilostomata.


Gen. 1. Membranipora, Blainv.

Area of cells rhomboidal; internal margin of the aperture denticulate ; cells separated by a narrow raised line.

Hab. Mazatlan : on the shells of Imperator olivaceus, I. unguis, and Anemia.

The outline of the cells is usually distinctly defined by a narrow brown line. One or two rounded or triangular eminences (probably ovicells) are visible on many of the cells in front and below....

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