N99

Botryostrobus aquilonaris (Bailey)

Eucyrtidium aquilonaris Bailey, 1856, p. 4, pl. 1, fig. 9

Eucyrtidium tumidulum Bailey, 1856, p. 5, pl. 1, fig. 11

Botryostrobus aquilonaris (Bailey), Nigrini, 1977, p. 246, pl. 1, fig. 1.

DESCRIPTION "Shell typically heavy, thick walled, but early forms are not so robust. Constrictions (other than collar and lumbar strictures) unevely spaced and all strictures usually obscure externally. Shell is spindle-shaped with 4 or 5 post-cephalic segments, the fourth being the widest. Cephalis hemispherical with small irregular pores; vertical tube robust, cylindrical, directed obliquely upwards at approximately 45°. Apical horn very small, needle-like. Thorax inflated with 2 or 3 transverse rows of large subcircular pores. Subsequent segments with 3 to 6 (usually 4) transverse rows of very closely spaced circular pores. The thickness of the shell makes each pore appear to have a ring around it. Shell narrows distally, terminating in a smooth peristome of variable width; peristome may have a single row of pores. Termination smooth or with an undulating margin." (from Nigrini, in press).

DIMENSIONS "Total length 110-155 microns; maximum breadth 60-90 microns." (from Nigrini, 1977).

REMARKS

1. For a more complete synonymy see Nigrini, 1977.

2. Benson's (1966) description and dimensions of this species (Siphocampium erucosum (Haeckel) in Benson, p. 527) are consistent with the above.

Plate 27, figure 1

N100

RECENT DISTRIBUTION

1. Benson, 1966 (Siphocampium erucosum); "...nearly cosmopolitan in the Gulf [of California] ... its sparse distribution in the northern Gulf and its slightly greater frequency and more general distribution in the southern Gulf indicate that is primarily an oceanic species."

2. Sachs, 1973, Code 17N (Siphocampe aquilonaris); "Widespread, with maximum occurrence about 6%."

3. Molina-Cruz, 1975, Code N33 (Siphocampe aquilonaris); used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent N33 at each station.

4. Robertson, 1975, (Siphocampe aquilonaris); "This species loads most heavily in factor 3 (transitional). At present it occurs most abundantly in the area north of about 40 degrees N with the exception of the Sea of Okhotsk where it is absent. At 18,000 YBP the abundance of this species is significantly reduced, especially to the north."