Type species:Cyrtocapsa mastoidea Yao (OD)
Description:Tetracyrtid, pear-shaped; segments outside not or only indistinctly separated each other. Cephalis poreless or with very few small pores. Postcephalic segments with very few small pores. Postcephalic segments with widely scattered small pores. Sutural pore very distinct. Distal appendix with large pores, but not separated from the distal segment by a ring of very large pores. Very tiny apical horn may be present. The appendix may have also a distal spine.
Remarks:The appendix in Japonocapsa is separated from the distal segment by a ring of very big pores and has otherwise small pores like the postcephalic segments. Unuma Ichikawa and Yao, 1976 has the same type of appendix, but this genus is multicyrtid and has strong longitudinal ribs. Yaocapsa n. gen. is a little transitional to the Syringocapsinae, Foreman 1973b, above all to "Syringocapsa" agolarium Foreman, 1973b that is otherwise not a typical representative of the Syringocapsinae. The wall structure and the presence of a sutural pore indicate that Yaocapsa n. gen. should be assigned to the Japonocapsinae n. subfam.
Stratigraphic range:Bajocian of Bukk Mts. and Japan. Middle Jurassic, Mesozoic.
Etymology:In honour of Prof. Dr. A Yao, Osaka, Japan, the author of the type species.
Subsequent descriptions:?

Description and dimensions:Shell of five segments. Cephalis spherical, poreless with a short apical horn. Internally, a branched vertical spine (as in Foreman, 1966, figs. 4-6) present. Thorax and abdomen together truncate-conical without stricture externally. Fourth segment truncate-subspherical with basal thickened-wall, and a constricted aperture or a central opening. Second to fourth segments with pores and smooth surface. Pores small, circular, arranged regularly and partly irregularly. Fifth segment small, cylindrical proximally and medianly, and hemispherical distally with a short spine in some specimens. Last segment with thin wall, and with large, circular pores.       (Based on 12 specimens) Height overall, 145-180µm, of cephalis 18-26µm, of thorax 20-27µm, of abdomen 20-32µm, of fourth segment 48-70µm, of fifth segment 25-37µm, of apical horn 1-5µm, of basal spine 2-15µm, maximum width of shell 67-98µm. Remarks:This species is characterized by the fifth segment which forms a basket-like shell and covers the aperture of fourth segment. It is doubtful that the fifth segment is an independent one. Repository:Holotype: OCU MR 2290 (IN 1-16), and paratype: OCU MR 2291 (IN 1-16), Department of Geosciences, Osaka City University, Japan.

Type locality:Manganese carbonate ore, Mino Belt, river side of the Kiso, east of Unuma, Kagamihara City, Gifu Pref, Central Japan.
Original stratigraphic range:Mesozoic.
Etymology:From the Latin mastoideus = mastoid.
Subsequent descriptions:?

Literature cited:- Foreman, H. P. (1966). Two Cretaceous radiolarian genera. Micropaleontology 12(3): 355-359.
- Foreman, H. P. (1973b). Radiolaria from DSDP Leg 20. Initial Reports of the Deep Sea Drilling Project. B. C. Heezen, I. D. MacGregor et al. Washington, D.C., U. S. Government Printing Office. 20: 249-305.
- Ichikawa, K. and A. Yao (1976). Two new genera of Mesozoic cyrtoid radiolarians from Japan. Progress in Micropaleontology, Special Publication. Y. Takayanagi and T. Saito. New York, USA, Micropaleontology Press, The American Museum of Natural History: 110-117.
- Kozur, H. (1984a). New radiolarian taxa from the Triassic and Jurassic. Geologisch - Paläontologische Mitteilungen Innsbruck 13(2): 49-88.
- Yao, A. (1979). Radiolarian fauna from the Mino Belt in the northern part of the Inuyama Area, Central Japan, Part II: Nassellaria I. Journal of Geosciences, Osaka City University 22: 21-72.