Parachasmatopora sp. A

(Figs 16G; 17 A-E)

MATERIAL EXAMINED. — CEGH-UNC 27526 a, CEGH-UNC 27529 b, CEGH-UNC 27533 a, CEGH-UNC 27545 a, b.

OCCURRENCE. — La Pola Formation, Upper Ordovician, Sandbian; La Pola creek section near Albardon village, San Juan Province, Argentine Precordillera, western Argentina.

DESCRIPTION

Exterior

Reticulate colonies consisting of regularly anastomosing branches. Branches rounded in cross section, 0.25-0.47 mm wide and 0.30-0.50 mm thick. Fenestrules elliptical, 0.22- 0.30 mm wide and 0.43-0.91 mm long. Autozooecial apertures rounded to oval, arranged in two alternating rows on branches, 3-4 in each fenestrule length, 0.05-0.09 mm in width.Low keel between autozooecial aperture rows carrying small elliptical nodes. Heterozooecia absent. Microstylets occurring both on reverse and obverse sides of colony, 0.02-0.03 mm in diameter.

Interior

Autozooecia long, rectangular in deep tangential section, occasionally having abundant diaphragms. Vestibule short. Hemisepta absent.Inner granular skeleton hyaline, 0.005 -0.008 mm thick. Outer lamellar skeleton usually well-developed on both obverse and reverse sides of colony, 0.075 - 0.040 mm thick.

COMPARISON

Parachasmatopora sp. A species differs from Parachasmatopora maennili Morozova & Lavrentjeva, 1981 in smaller autozooecial apertures (0.05-0.09 mm vs 0.10-0.12 mm in P. maennili). Superficially, Parachasmatopora sp. Ais similar to Parachasmatopora typicalis (Bassler, 1952). However, the latter species was only externally figured (Bassler 1952: figs 8-9). Therefore, a detailed comparison is impossible.