S103

Stylodictya validispina Jorgensen

Stylodictya validispina Jorgensen, 1905, p. 119, pl.10, fig. 40; Petrushevskaya, 1967, p.33, fig. 17, IV-V

DESCRIPTION "Skeleton in form of flat disk not thickened in middle. Central round chamber distinctly visible; around it four chambers of approximately equal dimensions arranged in form of cross. These surrounded by others, usually in larger dimensions, disposed in more or less regular concentric rings...; sometimes arrangement of chambers somewhat disturbed and zigzag seam present that may be regarded as proof of their spiral growth. Concentric rings of chambers number 5-6; their width hardly increases to periphery of disk. Pores on walls of chambers irregular, usually 2-2.5 pores located at width of one ring (i.e., third pore disposed in middle of seam between chambers of neighboring rings). Pores on peripheral rings somewhat larger than those on central. Growth of shell proceeds by successive growth of chambers around margin of disk. Adjacent rings pierced by radial pieces, some of which extend from margin of disks as radial needles. Apart from these, radial needles not connected with the radial pieces arise around margin of disk. Radial needles arranged very irregularly, number 12-16 along periphery of disk with five rings (most frequently broken off to base)." (translated from Petrushevskaya, 1967).

"The four central chambers so characteristic of this species were found to be less distinctive in the downcore study of RC14-105." (from Robertson, 1975).

DIMENSIONS

"Diameter of central chamber 12-15 microns, diameter of first ring 30-35 microns, diameter of second ring 55-60 microns, of third 80-85 microns, of fourth 110-115 microns, diameter of disk with five rings about 140 microns." (translated from Petrushevskaya, 1967)

These dimensions are in good agreement with those reported by Benson (1966) and Sachs (1973).

REMARKS

1. Petrushevskaya (1975) placed this species in synonymy with Stylodictya stellata Bailey. However, Bailey's illustration (1856, pl. 1, fig. 20) does not show the characteristic central girdles and for that reason the synonymy is rejected.

Plate 13, figures 5a, b

S104

RECENT DISTRIBUTION

1. Benson, 1966; considered together with S. aculeata; "...rare at all stations in the Gulf [of California] except at 64 where it is common (2.0%)."

2. Sachs, 1973, Code 13I; "Very widespread to 9% of the total fauna, but prefers Northern (Polar factor) conditions."

3. Molina-Cruz, 1975, Code S47; used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S47 at each station.

4. Robertson, 1975; "The species loads most heavily in factor 3 (transitional) but also loads in factor 1 (subpolar). The greatest abundances for this species are to the north of 40 degrees N at both the present and 18,000 YBP. There is not a marked shift in the abundance pattern from the present to 18,000 YBP but at 18,000 YBP abundances are higher north of 40 degrees N."