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....