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Species Globorotalia siakensis Le Roy 1939 | ||||||
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Iaccarino (1985): Globorotalia siakensis, a species widely used in the biostratigraphic record was regarded for a long time as a taxon not discernible from G. mayeri. Blow (1969) re examined the holotype of Cushman & Ellisor (1939) and reached the conclusion that the two species are not co specific. Of the same opinion were Stainforth et al. (1975) and many other authors. More recently Bolli & Saunders (1982a) in a revision of G. mayeri concluded that G. mayeri and G. siakensis cannot be maintained as separate taxa. The conclusions reached by these authors, discussed in the taxonomic notes of G. mayeri in this volume (Chapter 6), are based on the direct examination of the holotype of G. mayeri and on illustrations and documentations of G. siakensis. To demonstrate that their opinion is correct, they had the holotype redrawn. Bolli & Saunders (1982, pl. 1) provide three illustrations of the holotype of G. mayeri: the original one of Cushman & Ellisor (1939, figs. 7-9), that redrawn for Blow (1969, figs. 10-12) and, that redrawn for Bolli & Saunders (1982a, figs. 13-15). When comparing the three illustrations of the holotype it appears that they are closely comparable but are distinctly different from the holotype of G. siakensis, both as figured originally by LeRoy (1939) and later by Blow (1969). My direct examination of the holotype of G. siakensis deposited in Bandung (Java) confirms that the illustrations correspond well to the holotype. It is characterized by globose chambers not appressed against each other, a distinctly lobate equatorial periphery and an equally convex axial periphery. In G. mayeri, conversely, the chambers of the last whorl are radially elongated, appressed against each other, the equatorial periphery is distinctly weakly lobate and the axial periphery distinctly plano convex. The only deviation is that the intercameral sutures are not distinctly curved as stated by Blow (1969). It is therefore considered here that the two species have different features which justify their separation. This view is independent of the intercameral sutures. All the considerations reported by Bolli & Saunders for G. mayeri are applicable to G. siakensis. In fact, the variability observed in G. mayeri sensu Bolli & Saunders is also typical of G. siakensis, such as the shape of the aperture which can be a low or a high arch. G. siakensis also shows great variability in the number of chambers (from 4 1/2 to 6-7) with generally few in the lower part of its range. A trend could, however, not be established. According to Bolli & Saunders, G. continuosa is considered a variant of G. mayeri (G. siakensis for us) (see pl. 4 of Bolli & Saunders, 1982), but as a variant it should have the same range. On the contrary G. continuosa continues well above the extinction of G. siakensis. Srinivasan (1975): This species is distinguished from Globorotalia mayeri by its distinctly lobate equatorial outline and fairly high-arched aperture bordered by a rim. There is considerable variation in the number of chambers in the last whorl - from four and a half to six. Individuals with a kummerform last chamber closely resemble specimens of G. cf. bella illustrated by Jenkins and Orr (1972, pl. 20, figs. 7-8) from eastern equatorial Pacific deep-sea cores. |
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| Synonym list: | ||||||
| Iaccarino (1985): 1939 Globigerina siakensis Roy. - Le Roy : p.262 pl. 4, figs. 20-22
1985 Globorotalia siakensis Le Roy. - Iaccarino : p.305 figs. 6.11a-c; 4
Srinivasan (1975): 1939 Globigerina siakensis Roy. - LeRoy : p.262 pl. 4; fig. 20-22
1975 Globorotalia siakensis Le Roy. - Srinivasan : p.149 pl. 4; fig. 1-3
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| Was used in synonym list of: | ||||||
| References: | ||||||
Le Roy,L.W. (1939): LeRoy,L.W.. (1939): Srinivasan,M.S. (1975): Iaccarino,S. (1985): |
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| Anonymous: Unedited TaxonConcept data | ||||||
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