N87

Pterocorys minythorax (Nigrini)

Theoconus minythorax Nigrini, 1968, p. 57, pl. 1, fig. 8

DESCRIPTION

"Shell conical, rather thick-walled, smooth. Cephalis trilocular with relatively large subcircular pores and a short, 3-bladed apical horn, usually about 1\2 of the cephalic length. Primary lateral and dorsal spines continue as ribs in the thoracic wall for more than 1\2 of its length and may project to form small, thornlike wings. Collar stricture not pronounced.

"Thorax small, campanulate; pores subcircular, 8-10 on a half-equator, aligned longitudinally with very narrow intervening bars. Lumbar stricture distinct.

"Abdomen slightly flared, up to 3 times as long as thorax. Pores similar to those on thorax, 9-10 on a half-equator. Termination always ragged, mouth wide open...

"This species differs from other members of the genus Theoconus by its small thorax, relative to the size of its abdomen, and by its large pores. It was identified and described by Benson as Theoconus zancleus Muller, but T. zancleus is apparently not synonymous with the species here described. Also, it is thought that Benson's description encompasses 2 species; the specimen shown in plate 33, figure 5 appears to be the same as T. minythorax, but the one in plate 33, fig. 4 is not." (from Nigrini, 1968).

DIMENSIONS "Length of cephalis 27-36 microns, of thorax 36-45 microns, of abdomen 63-127 microns. Maximum breadth of cephalis 18-27 microns, of thorax 63-72 microns, of abdomen 90-118 microns." (from Nigrini, 1968).

Plate 25, figure 10

N88

RECENT DISTRIBUTION

1. Nigrini, 1968 (Theoconus minythorax), text-fig. 9; "Few to abundant in the regions of the North and South Equatorial and Peru Currents, but rare or absent in the region of the Equatorial Countercurrent."

2. Molina-Cruz, 1975, Code N7 (Theoconus minythorax); used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent N7 at each station.