CATALOG OF ORIGINAL DESCRIPTIONS: Globorotalia (Globorotalia) iwaiensis Takayanagi & Oda, in Takayangi et al. 1976
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Citation: Globorotalia (Globorotalia) iwaiensis Takayanagi & Oda, in Takayangi et al. 1976taxonomic rank: speciesType specimens: Holotype (IGPS 75027) & Paratype (IGPS 75028)Type sample (& lithostrat): sample IWA-15, in the Shimokurosawa FormationType locality: southern bank of the lwai River, 600 m. downstream from the junction of the lwai and Kubo rivers. Kamikurosawa, lchinoseki City, lwate Prefecture; JapanType repository: Sendai, Japan; Tohoku University Institute of Geology and Paleontology
Original Description Test large. low trochospiral. biconvex. compressed, strongly convex on umbilical side. less convex on spiral side; equatorial periphery slightly lobulate; axial periphery acute, with a thin but distinct carina; chambers angular, more or less flat, slightly elongate and curved on spiral side, high on umbilical side; about 15 to 16 chambers arranged in three whorls; four and a half to five chambers in the last whorl. increasing gradually in size; sutures gently curved and limbate on spiral side, radial to slightly curved and depressed on umbilical side; umbilicus very narrow and closed; wall calcareous, finely perforate; surface smooth except for umbilical surface and peripheral margin of earlier chambers in the last whorl, which are covered with pustules; aperture interiomarginal, umbilical-extraumbilical, a low arch, bordered by a lip. Size: Maximum diameter of holotype (plate 1. figures 2a-2c) 0.30 mm., thickness 0.15 mm. Maximum diameter of paratype (plate 1. figures 3a-3c)
0.40 mm.. thickness 0.20 mm. Unfigured paratypes range from 0.16 to 0.30 mm. in diameter. Extra details from original publication Remarks: Although a sufficient number of specimens ot the present species were found from the Shimokurosawa Formation in the lchinoseki area, specimens from the lsohara Formation of the Joban coal field were also studied. Compared with the specimens from the type are, the lsohara ones show more typical characters which are developed on only fully adult forms. lt seems remarkable that G. (G.) iwaiensis presents a closer similarity to some Upper Miocene species recorded from the temperate water biofacies of the Southern Hemisphere. This species is, however, distinguished from G. (G.) miotumidamiotumida Jenkins by possessing a larger test and four and a half to five chambers in the last whorl instead of only four as in the latter species. The species is also close to G. (G.) conomiozea Kennett, but differs from the latter in having a more convex spiral side. a less vaulted umbilical side, and more chambers in the last whorl. Fully adult forms. such as the figured paratype of the present species, bear some similarity in appearance to G. (G.) praemenardii praemenardii Cushman and Stainforth. The new species has. however, a relatively highly arched aperture and a higher test than the latter. The ratio of the spiral umbilical height of the test to the length of the maximum diameter is about 1 : 2 in G. (G.) iwaiensis, whereas it is about 1 : 3 in G. (G.) praemenardii praemenardii (fide Blow, 1969, p. 368) .
Occurrence: Individuals of this species are found from the lsohara and Shimotezuna formations in the southern part of the Joban coal field (lbaragi Prefecture), in addition to the Shimokurosawa Formation.
References:
Takayanagi, Y., Takayama, T., Sakai, T., Oda, M. & Kitazato, H. (1976). Microbiostratigraphy of some Middle Miocene sequences in northern Japan. In, Takayanagi, Y. & Saito, T. (eds) Progress in micropaleontology. Micropaleontology Press, New York 356-381. gs
Globorotalia (Globorotalia) iwaiensis compiled by the pforams@mikrotax project teamviewed: 4-12-2023
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