Diplotrypa undefined-a

Diplotrypa sp. A

(Fig. 9G; 10 A-D; Appendix 1)

MATERIAL EXAMINED. — Single colony (two thin sections) CEGH-UNC 27543a, b.

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

DESCRIPTION

Massive colony, 6.2-6.4 mm in thickness, with indistinct endozone. Autozooecia growing from epitheca at high angles. Autozooecia in outer exozone often developing from mesozooecia. Autozooecial diaphragms common to rare, planar, curved proximally, irregularly spaced in autozooecia. Mesozooecia common, up to 3 surrounding each autozooecial aperture, bearing abundant straight diaphragms. Autozooecial walls fine fibrous microstructure, 0.005 -0.010 mm thick in endozone and 0.02-0.03 mm thick in exozone.

COMPARISON

Diplotrypa sp. A is similar to Diplotrypa catenulata Coryell, 1921 from the Sandbian of United States. Coryell [1921: 296] gave only the spacing of 4-4.5 apertures per 2 mm (distance from centre to centre 0.44-0.50 mm), which is more than double as large as the aperture spacing of the present material (average distance from centre to centre 0.22 mm). Size of apertures for Diplotrypa catenulata recorded by Astrova (1965: 185-186) from the Middle Ordovician of Arctic, was given as 0.42-0.75 mm (with macrozooecia of 0.9-1.0 mm width). Diplotrypa sp. A is similar to D. pusilla Astrova, 1965 from the Lower Ordovician of the Russian Arctic, but differs from it by less abundant diaphragms in autozooecia.