. Bulletin - United States National Museum. Science. 178 BULLETIN 100, UNITED STATES NATIONAL MUSEUM entire surface. Opesia and orifice practically coextensive, widely separated from the distal end of the area, with a raised oral arch and a distinct median process. Avicularia and ovicells unknown. Genotype.—A. obliquum Harmer, 1926. Recent. Family MEMBRANICELLARIIDAE Levinsen, 1909 The ovicells, situated on the distal part of each zooecium, are inner spaces in the frontal wall of the zooecia and open outwards through a variously shaped opening. The frontal and the dorsal of each zooecium have
. Bulletin - United States National Museum. Science. 178 BULLETIN 100, UNITED STATES NATIONAL MUSEUM entire surface. Opesia and orifice practically coextensive, widely separated from the distal end of the area, with a raised oral arch and a distinct median process. Avicularia and ovicells unknown. Genotype.—A. obliquum Harmer, 1926. Recent. Family MEMBRANICELLARIIDAE Levinsen, 1909 The ovicells, situated on the distal part of each zooecium, are inner spaces in the frontal wall of the zooecia and open outwards through a variously shaped opening. The frontal and the dorsal of each zooecium have not the same form. There are avicularia or interzooecial onychocellaria. The opesium is surrounded by a raised rim with only the distal part filled by a membranous opercular valve; it perforates the cryptocyst. Structure.—The ovicell is hyperstomial but never placed on the distal zooecium; it is formed by the development of the mural rim. The opercular valve has a membranous frontal surface, but a well chitinized and strongly developed opercular arch. The membrane covering the aperture has on either side toward the center a parietal muscle attached to a very fine sclerite. The opesium is completely surrounded by the cryptocyst; it is median or anterior, but never terminal as in the Biflustridae and Onychocellidae. Classification.—Levinsen cited only the genus Membranicellaria. He refers here correctly a number of Cretaceous species whose structure is thus explained. But the list he gives is absolutely identical with that which Jullien, 1881, gave for his genus Dictuonia. It is convenient to preserve the latter name because of the presence of onychocellaria. The latter have persisted in the long succession of the ages as Vincularia maorica from the Philippines is provided with them. The known genera of the Membranicellariidae are as follows: Membranicellaria Levinsen, 1909. The interzooecial organs are avicularia with wide mandibles. Genotype.—Membranicellaria (Melicerit
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