S45

Hexacontium enthacanthum Jorgensen

Hexacontium enthacanthus Jorgensen, 1899, p. 52, pl. 2, fig. 14, pl. 4, fig. 20

Hexacontium entacanthum Jorgensen, Benson, 1966, p. 149, pl. 3, figs. 13, 14, pl. 4, figs: 1-3

DESCRIPTION "Cortical shell generally spherical but varies from subspherical to suboctahedral and in a few specimens has a subquadrate outline; surface ranges from completely smooth to generally one with thorns or thin conical by-spines which arise at the nodes of intervening bars as well as along the bars; in one specimen the by-spines branch and anastomose distally at a common distance from the cortical shell to form a secondary outer shell; pores subcircular or subelliptical, subpolygonal, or in a few tests with irregular shapes, subequal in size in most test but in a few with unequal size, with subregular (hexagonal) to irregular arrangement, with or without polygonal frames, in most specimens 8-9 on the half circumference but ranging from 7-13. Second shell spherical to subspherical, thin-walled, with surface ranging from smooth to one with scattered thorns or thin conical spines which in a few specimens join with the cortical shell to form thin secondary beams; pores subpolygonal to polygonal, unequal to subequal in size, with irregular to subregular arrangement, generally 6-8 on the half circumference but ranging from 5-10. First shell thin-walled, subspherical to suboctahedral, with 2-3 relatively large polygonal pores on the half-circumference. Each of the six mutually perpendicular radial beams arise from the corners of the suboctahedral inner shell, remain thin and cylindrical until they pierce the second shell after which they are relatively heavy and three-bladed in section. Beams continue beyond cortical shell as relatively heavy and in several specimens very long three-bladed spines, all six nearly of equal length and breadth. In several specimens not all beams and spines are mutually perpendicular; some specimens have seven or eight beams, the extra beams representing either bifurcations of one or more of the six primary beams at the level of either the first or second shell or separate beams arising from the first shell and with no regular relationship to the six primary beams; a few specimens observed with only five of the six primary beams present." (from Benson, 1966).

DIMENSIONS "diameter of cortical shell 74-154 microns, of second shell 30-50 microns, of first shell 12-22 microns; average length of main spines per specimen 9-112 microns." (from Benson, 1966).

REMARKS

1. Erroneous spelling in Benson (1966) has been repeated by numerous subsequent investigators.

Plate 5, figures 1a, b

S46

RECENT DISTRIBUTION

1. Benson, 1966; "This species is present at all stations in the Gulf [of California] except 214. It is one of the most abundant spumelline species found in the Gulf sediments... Its rare or nearly rare occurrence in the southern Gulf and its general increase northward indicates that it is a normal member of the tropical Pacific oceanic fauna and that it inhabits water masses with slightly higher salinity and temperature."

2. Sachs, 1973, Code 6S (Hexacontium spp.); "Forms encountered in the present study generally fitted Benson's descriptions of H. enthacanthum and H laevigatum, but were not divided. Shell spherical to subquadrate, smooth to hexagonally-framed pores, generally six mutually perpendicular spines, but a seventh occasionally present. Spines variably developed, but about a length of outer shell radium...

"Strongly Southern [south of about 45 degrees N], with maximum frequency to 5%. (There is also a Northern Hexacontium, which was mixed with Actinomma sp. in this study)."

3. Molina-Cruz, 1975, Code S17; used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S17 at each station.

4. Robertson, 1975, (Hexacontium spp.);

"The description of this genus as given by Benson (1966) was followed but the innermost shell was frequently very difficult to discern. All forms in this genus are counted except those forms in which the outer shell was subquadrate rather than spherical.

"This genus loads most heavily in factor 3 (transitional). At present its higher abundances generally occur south of 45 degrees N. At 18,000 YBP comparable abundances are found south of 40 degrees N."