Catalog - Rugoglobigerina (Rugoglobigerina) arwae

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Rugoglobigerina (Rugoglobigerina) arwae

Citation: Rugoglobigerina (Rugoglobigerina) arwae El Naggar 1971

Type specimens: Pl. 15, figs. 2, 3, 5-9

Type sample (& lithostrat): Esna Group, Sharawna Shale Formation

Type age (chronostrat): Upper Cretaceous, Maastrichtian

Type locality: Section at Wadi El-Sharawna. on the western slopes of Gebel Owaina, Esna-Idfu region of the Nile Valley, Upper Egypt.

Diagnosis: A Rugoglobigerina (Rugoglobigerina) with a small to medium sized, low trocho- piral, closely coiled test; very small initial whorl, and large later one with 4-5 rapidly increasing chambers, curved, depressed dorsal sutures, small to medium sized umbilicus and moderately developed meridional costellae.

Description: Test medium-sized, coiled in a low trochospire; dorsal side almost flat, with a slightly depressed inner part; ventral side inflated; equatorial periphery roughly quadriglobular, subovoid, lobate; axial periphery rounded; chambers on the dorsal side about 10, arranged in 2 very closely coiled dextral whorls; the initial chambers are very small, globigerine and increase slowly in size as added; chambers in the outer whorl 4, globigerine inflated, much larger than the early ones and increase more rapidly in size; the 4 globigerine, inflated chambers on the ventral side increase very rapidly in size as added; sutures on the dorsal side curved, depressed; on the ventral side they are slightly curved to almost straight, radial, depressed; umbilicus medium sized, covered by a complex system of tegilla which are only partially preserved; primary aperture interiomarginal, umbilical, covered by tegilla; surface rugose with large stout spicules arranged in a meridional pattern on the chambers of the outer whorl; wall calcareous, perforate, hyaline, except for the imperforate tegilla and surface rugosity.

Holotype: Maximum diameter 0. 375 mm., minimum diameter 0.336 mm., thickness 0.150 mm

Remarks. - Rugoglobigerina (R.) arwae El-Naggar differs from both R. (R.) ornata Bronnimann and R. (R.) rugosa (Plummer) [Globigerina rugosa, 1927] by its smaller, thinner, more closely coiled test; much smaller early part, and less rapidly increasing chambers in the outer whorl; smaller umbilicus; more curved, depressed sutures; less rugose surface and less developed meridional costellae. The rugosity on R. (R.) arwae is in the form of stout spicules with pointed ends (figs. 3a, 5a) while those on both the ornata and rugosa species are in the form of large pustules which are somewhat elongated to nearly coalesce and give the well developed appearance of meridionally disposed costellae. Transitional stages between the three species rugosa, ornata and arwae have been recorded, but nevertheless, their separate identity cannot be overlooked.

Stratigraphical range - Rugoglobigerina (R.) arwae is recorded to occur commonly in both the Middle and Late Maastrichtian "Globotruncana gansseri and Globotruncana esnehensis Zones" of the Esna-Idfu region, Nile Valley, Egypt, U.A.R.

References:

El-Naggar, Z. R. (1971b). The genus Rugoglobigerina in the Maastrichtian Sharawna Shale of Egypt. In, Farinacci, A. (ed.) Proceedings of the Second Planktonic Conference, Roma 1970. Edizioni Tecnoscienza 477-537. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Rugoglobigerina (Rugoglobigerina) arwae El Naggar 1971

Rugoglobigerina (Rugoglobigerina) arwae

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