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Pentactinosphaera hokurikuensis (Nakaseko, 1955)

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Melittosphaera (Melittosphaera) hokurikuensis
Description: Shell entirely globular, with two concentric spheres; the medullary shell in the radio of about 0.2 diameter, its pores large, circular, uniform in size, well spaced, very deeply set into the thick wall, with thin bars, and thin hexagonal frames; the wall of the cortical shell, with short sepaloid points at nodes of the hexagonal meshworks; the medullary shell very small, with three pores across the diameter, these pores large, hexagonal, uniform in size, and with thin bars; radial beams at least a dozen in number.
Measurements of the illustrated specimen: Diameter of the cortical shell 130µm, of the medullary shell 25µm, of the pores of the cortical shell 14µm, of the pores of the medullary shell 8µm, thickness of the wall 16µm.
Remarks: Melittosphaera hokurikuensis n. sp. is thicker than any other species belonging to the subgenus. M. tonamiensis n. sp. differs from this species in having the thinner wall and the smaller pores. Carposphaera infundibulum Haeckel (1887, p. 72 = Haliomma infundibuliforme Stöhr, 1880, p. 87, Taf.1, fig.6) described from the North Atlantic, Station 354 and the Tertiary rocks of Barbados and Sicily, has very thick wall, but its pores are hexagonal and have the thick bars.
Locality: B1, Nishidojima mudstone.
Nakaseko 1955
Pentactinosphaera hokurikuensis
Emended description: Outer shell globular, thick-walled with rough surface frequently arising bristle-like short by-spines along the wall inside cylindrical pores. Inner wall of outer shell quite smooth with round pores. Some specimens seem to consist of double outer shells by the wall structure of broken shell (see pl.l, fig. 3). Inner shell nearly spindle shaped with distinct four openings composed of five spines at the apical portion. Four lateral spines originate from the intermediate of four basal spines and extend to the wall inside outer shell. On the opposition of apical portion there is latticed shell composed of delicate, thorny bars with an antapical spine. Six spines connect to the outer shell as radial beams. They are rod-like, thorny except the antapical spine and slightly curved.
Remarks: This species is variable in size of outer shell and thickness of the wall, however, the internal skeleton is always the same. As mentioned above, the wall structures of some specimens appear to consist of double outer shells. It is, however, uncertain herein whether it is due to the process of the growth of the same species or shows quite different species.
Nakaseko et al 1983











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