Catalog - Eoglobigerina edita praeedita

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Eoglobigerina edita praeedita

Citation: Eoglobigerina edita praeedita Blow 1979

Type specimens: PM PF 63572 PM PF 63573 PM PF 63683 PM PF 63588 Pm Pf 63615 PM PF 63572

Type age (chronostrat): Basal Paleocene, lowermost Danian, zone Pa (Globorotalia (Turborotalia) longiapertura partial-range zone).

Type locality: DSDP Site 47/2 cored at a depth of 2689 meters on the Shatsky Rise, lat. 320 26.9' N. , long. 1570 42.7' E. , northwestern Pacific Ocean; holotype (fig. 6) and paratype (fig. 5) from sample I l6, 148-150 cm; paratype (fig. 9) from sample I l5, 148-150 cm; paratype (fig. 4) from sample I l4, 148-150 cm

The small test is coiled, in a low, fairly lax, trochospire with about 12-14 chambers comprising the spire and with five chambers present in the last convolution of the test; the penultimate whorl of chambers appears to consist of 6 chambers. In dorsal aspect, the chambers are moderately inflated, subglobular, but are appressed, closely-set and slightly embracing. The dorsal intercameral sutures are subradially disposed and, in equatorial profile, the test is lobate but sensibly circular in outline since the chambers enlarge only slowly in the progression of the trochospire. In ventral aspect, the chambers are inflated but closely-set, appressed and somewhat embracing. The ventral intercameral sutures are radially disposed and are incised to broadly depressed. The umbilicus is open, but shallow, and only moderately delimited by the umbilical shoulders of the last convolution of chambers. The aperture is interiomarginal, asymmetrically umbilical-extraumbilical and is a quite highly arched opening with a weakly developed porticus. The axial profile shows a rounded peripheral margin and no distinct dorsal convexity due to the low trochospire. The wall texture shows the mural-pores opening into distinct pore-pits but the inter-pore ridges are not well defined.

Maximum diameter of holotype 0.120 mm as measured electronically.

Remarks. As noted in the discussion given [Blow, 1979, op. cit., pp. 1210-1212] for Eoglobigerina edita edita (Subbotina) [Globigerina edila, 1953], two morphogroups can be distinguished for forms having a five-chambered last whorl which are broadly referable to Subbotina's taxon in a sensu lalo form. These two morphogroups are mainly distinguished on the relative height of the trochospire and the degree of tightness of the coiling-mode. In the forms referred to E. edita praeedita Blow, 1979, the paratype figured in fig. 5, in slightly oblique dorsa) view, shows the typical nature of the dorsal test and, especially, the nature of the earlier trochospire. Thus, in praeedita, as distinct from edila (sensu stricto), the early trochospire is depressed so that the dorsal surfaces of the earlier chambers do not stand much above the level of the dorsal surfaces of the later chambers in the last convolution of the test. Furthermore, the specimens referable to praeedita usually show a penultimate whorl of 6 chambers prior to the normal 5-chambered last whorl. On the other hand, E. edita edita (Subbotina) consistently appears to possess five-chambered penultimate and ultimate whorls.
The aperture is, like the condition seen in E. edita edita, variable in shape and position. However, usually the aperture is more laterally restricted than seen tn representatives of Subbotina's taxon. Nevertheless, the aperture consistently extends asymmetrically from the umbilicus towards the anterior side of the last chamber. As noted above, the essential differences between E. edita edita and E. edita praeedita may be noted and assessed from an evaluation of the dorsal aspect of the taxa. Thus, the paratype illustrated in fig. 4, also shows the 6-chambered penultimate whorl and the rather depressed initial spire. It is interesting to note that this 6-chambered penultimate whorl shows a similar chamber arrangement to that seen for small specimens of Rugoglobigerina hexacamerata Brönnimann (see Blow, 1979 op. cit., p. 1365).

References:

Blow, W. H. (1979). The Cainozoic Globigerinida: A study of the morphology, taxonomy, evolutionary relationships and stratigraphical distribution of some Globigerinida (mainly Globigerinacea). E. J. Brill, Leiden. 2: 1-1413. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Eoglobigerina edita praeedita Blow 1979

Eoglobigerina edita praeedita

References:

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