N103

Phormostichoartus corbula (Harting)

Lithocampe corbula Harting, 1863, p. 12, pl. 1, fig. 21

Siphocampe corbula (Harting), Nigrini, 1967, p. 85, pl. 8, fig. 5; pl. 9, fig. 3

Phormostichoartus corbula (Harting), Nigrini, 1977, p. 252, pl. 1, fig.

10 DESCRIPTION

"Shell thin-walled, smooth, subcylindrical, consisting of 4 segments of which the fourth is the broadest. Cephalis approximately spherical with a well-developed, poresless [vertical] tubule which curves downwards so as to lie close to the thorax; numerous subcircular pores; no apical horn. Collar stricture indistinct.

"Thorax short, truncate conical, with circular to subcircular pores arranged approximately in transverse rows. Lumbar and post-lumbar strictures distinct.

"Abdomen annular, somewhat longer than thorax. Pores small, subcircular to squarish, arranged in 5-8 regular closely spaced transverse rows.

"Fourth segment 2-4 times as long as abdomen; pores similar in size and shape to those on abdomen, in 9-17 transverse rows. Segment tapers slightly distally and ends in a generally poreless peristome. Termination smooth." (from Nigrini, 1967).

DIMENSIONS "Total length 130-165 microns; maximum breadth 65-75 microns. Measurements given by Nigrini (1967) have a greater range for both length and breadth." (from Nigrini, 1977).

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

2. Benson's (1966) description and dimensions of this species (Siphocampium cf. polyzona Haeckel in Benson, p. 513) are consistent with the above.

Plate 27, figure 3

N104

RECENT DISTRIBUTION

1. Benson, 1966 (Siphocampium cf. polyzona); "...rare but nearly cosmopolitan in the Gulf [of California]".

2. Nigrini, 1967, fig. 45 (Siphocampe corbula); "Indian Ocean occurrences - S. corbula is sparsely distributed in both low and middle latitudes, occurring in somewhat greater numbers (up to 3% of the described population) in the former."

3. Nigrini, 1970, fig. 36 (Siphocampe corbula); belongs to a tropical assemblage derived by recurrent group analysis of North pacific samples, but the species does range as far north as 40 degrees N in the western Pacific.

4. Molina-Cruz, 1975, Code N32 (Siphocampe corbula); used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent N32 at each station.