N89

Pterocorys zancleus (Muller)

Eucyrtidium zanclaeum Muller, 1858, p. 41, pl. 6, figs. 1-3

Theoconus zancleus (Muller), Benson, 1966, p. 482, pl. 33, fig. 4 (non fig. 5)

DESCRIPTION

"Structure of the cephalis including prominent dorso-lateral lobes, a straight dorsal face merging with a three-bladed apical horn, four collar pores, and the presence of three indistinct thoracic ribs extending as short spines above the base of the thorax the same as in the four preceding species. Cephalis closed at the top, with smooth surface and small, unequal to subequal, circular pores. Vertical spine indistinct but present; apical horn not robust. Thorax campanulate to truncate-conical, separated from the cephalis above by a change in contour and from the abdomen below by a distinct constriction(1) occupied by an internal septal ring. Surface of thorax smooth. Thoracic pores ranging from circular and subequal to subpolygonal and increasing slightly in size distally with regular hexagonal arrangement in longitudinal rows. Abdomen smooth, ranging from subcylindrical with its distal portion tapering inward and with equal (6-12 microns), circular pores arranged hexagonally in longitudinal rows to truncate-conical with distal portion broader and not constricted and with polygonal to subpolygonal pores having the same arrangement but gradually increasing in size distally (from about 6-8 microns, to 20-26 microns)." (from Benson, 1966).

(1) The present authors have not noted a distinct lumbar constriction.

DIMENSIONS

"Length of cephalis 21-39 microns, of thorax 36-49 microns, of abdomen 37-143 microns; breadth of cephalis 21-32 microns, of thorax 64-80 microns of abdomen 75-119 microns; length of apical horn 9-36 microns, of vertical spine 0-5 microns, of dorsal and primary lateral spines 0-12 microns (from Benson, 1966).

"overall length excluding horn, 134 +/- 16 microns; thorax length, 50 +/- 60 microns, thorax width, 78 +/- 4 microns, abdomen width, 91 +/- 9 microns; abdomen length, 59 +/- 11 microns" (from Sachs, 1973).

REMARKS

1. For a more complete synonymy see Benson (1966). Note, however, that the specimen figured by Benson on P1. 33, fig. 5 is probably P. minythorax (Nigrini). Benson apparently combined these 2 species in his description, dimensions and distribution.

Plate 25, figures 11a,b

N90

RECENT DISTRIBUTION

1. Benson, 1966 (Theoconus zancleus)i "a common member of the Gulf [of California] assemblage, but its average frequency is greater in the southern half of the Gulf than in the northern half."

2. Sachs, 1973, text-fig. 2G, Code 21N (Theoconus zancleus); "Essentially confined to the Southern region (beneath Transitional waters), where it may reach abundances of 14%."

Sachs (personal communication) counted only P. zancleus. P. minythorax was not observed by him in North Pacific sediments.

3. Molina-Cruz, 1975, Code N40 (Theoconus zancleus); used in factor analysis of southeast Pacific assemblages) cf. Appendix 10 for percent N40 at each station.

4. Robertson, 1975, text-fig. 2G (Theoconus zancleus)i "This species loads quite heavily in factor 3 (transitional). At present its highest abundances occur in a band between 35 degrees and 45 degrees N. At 18,000 YBP the zone of highest abundance is shifted to the south."