Catalog - Porticulasphaera beckmanni

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Porticulasphaera beckmanni

Citation: Porticulasphaera beckmanni Saito 1962

Type specimens: Plate 34 figures 1a-2; holotype (fig. 1), no. 79016; and paratype (fig. 2),no. 79017.

Type sample (& lithostrat): Globigerina tuff; in a light greenish gray tuffaceous compact medium to fine grained sandstone.

Type age (chronostrat): Eocene, Lutetian

Type locality: Sea cliff of Onion Beach, at the east side of the small embayment of Oki-mura, Haha-jima Island, Ogosawara Group, Japan (lat. 26°40' N., long. 138°10' E.).

Type repository: Sendai; Institute ofGeology and Paleontology, Tohoku University, Sendai, Japan

Test free, subglobular, early portion low trochospiral, with five to six chambers per whorl, last chamber subglobular, inflated and strongly embracing and enveloping umbilical region of early coil, more in extent than half of entire test; sutures usually distinct, depressed and somewhat incised; wall calcareous, comparatively thick, coarsely perforate; primary aperture in early portion interiomarginal, umbilical which is covered by last enveloping chamber with smaller multiple secondary apertures around its its lower margin, secondary sutural apertures also visible on spiral side of early portion as in Globigerinoides.

Maximum diameter of holotype 0.60 mm, paratype 0.54 mm. Other specimens range from 0.44 to 0.62 mm in maximum diameter.

Remarks: As noted under Globigerapsis mexicana (Cushman), this species was described from the Oceanic Formation of Barbados as Globigerinoides mexicana (Cushman) by Beckmann (1954, loc. cit.) and as Porticulasphaera mexicana (Cushman) by Bolli et al. (1957) and Bolli (1957) from the Eocene Navet Formation, Trinidad. But the characters are different from Cushman's original mexicana and this new name which represents the hypotypes of Bolli et al. and of Beckmann is here proposed. Porticulasphaera beckmanni Saito, 1962, differs from Globigerapsis mexicana (Cushman) in having the inflated hemispherical last chamber enveloping the umbilical region ofthe early coil, larger in size than the entire previous portion of the test, and the multiple sutural supplementary apertures around the lower margin of the last chamber, at the contact with the sutures of earlier coils. It is also distinguished by the secondary sutural apertures on the spiral side as in Globigerinoides.

According to Bolli (1957), this species seems to have its range comparable with his Porticulasphaera mexicana Zone (herein treated as Porticulasphaera beckmanni Zone).

References:

Premoli Silva, I., Wade, B. S. & Pearson, P. N. (2006). Taxonomy, biostratigraphy, and phylogeny of Globigerinatheka and Orbulinoides. In, Pearson, P. N., Olsson, R. K., Hemleben, C., Huber, B. T. & Berggren, W. A. (eds) Atlas of Eocene Planktonic Foraminifera. Cushman Foundation for Foraminiferal Research, Special Publication . 41(Chap 7): 169-212. gs O

Saito, T. (1962a). Eocene planktonic foraminifera from Hahajima (Hillsborough Island). Transactions and Proceedings of the Palaeontological Society of Japan. 45: 209-225. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Porticulasphaera beckmanni Saito 1962

Porticulasphaera beckmanni

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