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Amphistylus angelinus (Campbell and Clark, 1944)

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Stylosphaera (Stylosphaerella) angelina
Shell large, globular, with spiny surface and two equal, opposite polar spines at least as long as diameter of shell and sometimes longer, rather thick (about 0,06 their length in diameter), circular in section, bases with about 12 short, vertical ridges, and blunted tips with the subadjacent sides roughened; cortical and medullary shells both spherical, latter nearly 0,5 diameter of former; supporting beams obscure because of great density of cortical shell; wall of cortical shell thick (at least 0,15 trans-diameter), extremely dense, wall of medullary shell thinner; surface of cortical shell spiny, by-spines arising as sepaloid points from pore-framework so that whole surface is like a burr, some of by-spines anastomosed and forming a sort of cactus-like feltwork raised above general shell-surface, medullary shell smooth; pores of cortical shell subuniformly subcircular, 36 or more around a diameter, rather closely and deeply set into thick lattice-framework, from outer surface of which arise by-spines (their length generally greater than 0,8 length of polar spines), pore-framework with funnel-shaped apertures, pores of medullary shell smaller and less numerous than those of cortical shell, less in diameter than shell-substance which separates them. Length total, 300μ, of polar spines, 110μ; diameter of cortical sphere, 80μ, of its pores, 8,8μ.
Stylosphaera angelina n.sp. differs from setosa (Ehrenberg, 1872) in possessing subcircular, rather than subhexagonal, and more numerous pores, and a thick wall. Medullary shell larger than in latter. Almost exactly like Xyphosphaera pallas (Haeckel, 1887, pl.14, fig.4), save that there are two concentric spheres rather than one. This Miocene species is apparently a virile, pelagic form adapted, in presence of long polar spines and bristly surface, to flotation near surface of sea.
Campbell & Clark 1944
Shell composed of two medullary shells and one cortical shell. Inner medullary shell irregular with 3-4 polygonal pores across a diameter. Outer medullary shell approximately spherical, with 7-9 circular pores of equal dimensions across a diameter, connected to cortical shell by two bars collinear with the polar spines, and by 6-11 randomly distributed bars. Cortical shell spherical or slightly ellipsoidal, medium to thick-walled, covered by small conical spines of variable length, with small circular, regularly disposed pores of uniform size. Polar spines slenderly conical, unequal in length, commonly not aligned along the polar axis.
Measurements based on 40 specimens from Samples 274-21, CC; 266-16-2, 100-102cm; 266-15, CC; 266-14, CC; and 266-14-1, 51-53cm: diameter of the cortical shell, 117-154; of the outer medullary shell, 30-37; and of the inner medullary shell, 25-30; length of the polar spine, 145-171.

Remarks:
This species differs from Stylatractus universus Hays in having conical spines which are not extensions of radial spines, and in having a more spherical cortical shell. These differences are conspicuous enough to seperate them even though transitional forms have been observed in the upper Miocene and lower Pliocene sediments. Kling included S. universus (1973, pl. 1, fig. 14-17; pl. 6, fig. 14-17) and this form (pl. 6, fig. 18) as Axoprunum angelinum. The specimens in antarctic sediments have three concentric shells and polar spines of unequal length; thus they belong to genus Amphistylus.
Chen 1975


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