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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 (Melicerita) dubia Busk, 1885. Re- 

 cent. 



Omoiosia Canu and Bassler, 1927. The interzooecial organs are 

 straight onvchocellaria. 



Fig. 52. — Genus Atelesto- 

 zoum Harmer, 1926 



Zooecia of A. obliquum 

 Harmer, 1926, magnified. 



