Stainforth, R. M.,
The Micropaleontologist 1953 - 7:4:23
In recent years several new records of Globigerina mexicana Cushman have appeared, indicating the wide geographic spread of this distinctive species. All the records have been in Middle to Upper Eocene beds, hence this species deserves recognition as a potential key marker comparable in status to Hantkenina spp.
With this in mind, the writer has been watching for Globigerina mexicana in Peruvian material, and was recently gratified to find a single, but excellent, specimen in a fauna from the Chira shale. It is noteworthy that figures of the species from various localities show close agreement with the type figure (a situation unfortunately rare in the Globigerinas), and identification of the solitary specimen is made with complete confidence.
Records of Globigerina mexicana Include:
Dominican Republic: Probably Upper Eocene; base of Tabera formation. See Bermúdez 1949.
Trinidad: Middle and Upper Eocene; formations not specified. See Bolli 1951.
Bonaire (N. W. I.): Upper Eocene; unnamed marl. See Drooger 1953.
Peru: Upper Eocene; Chira formation. Here placed on record; sec figures 1-3.
Switzerland: Upper Eocene; Stadschiefer. See Bolli 1951.
Middle to Upper Eocene; Localities and formations not specified. See Grimsdale 1951.
Horizon and Hess Guyots: Eocene; in submarine cores. See Hamilton 1953.
Eocene; details unspecified. Apparently Parr recorded Globigerina orbiformis Cole, but Thalmann considered the specimens to be Globigerina mexicana. See Finlay 1939.
Figures 1-3. Globigerina mexicana Cushman. Specimen from the Chira shale. Peru. Outline drawings to show chamber arrangement: the whole shell surface is finely cancellate. Diameter 0.40 mm.
Globigerina mexicana appears to be correctly assigned to Globigerina, even allowing for modern subdivision of the Globigerinidae into Globigerinoides, Globigerinella, Globoquadrina and others included by earlier authors in one all-embracing genus, Globigerina. In particular, no grounds are seen for placing it in Globigerinoides, an allocation used by several of the authors cited below. Cushman’s type description (1927b) of Globigerinoides is awkwardly worded (“…as Globigerina with numerous large, supplementary, apertures around the margin of the chamber, opening into the umbilical area…”). This was later modified (Cushman 1948) to “…numerous large, supplementary apertures around the margin of the chamber, opening Into the chamber, and some of them into the umbilical area…” Judging from the type species chosen (Globigerinoides ruber) and from Cushman’s subsequent inclusion of Globigerinoides sacculifer, G. triloba, G. conglobatus, etc., in Globigerinoides, a more lucid wording might have been “…numerous large supplementary apertures along the spiral suture, opening dorsally Into the adult chambers.” In any case the presence of numerous large supplementary apertures Is a key feature of Globigerinoides, hence the present writer is opposed to the inclusion of Globigerinas with merely open or gaping sutures (Globigerina mexicana, Globigerina grimsdalei) in Globigerinoides.
BERMÚDEZ, P. J.
1938 - Soc. Cubana Hist. Nat., Mem., vol. 12. p. 10.
1949 - Cushman Lab. Foram. Res. Spec. PubI. 25. p. 279. pl. 21. fig. 44.
1950 - Soc. Cubana Hist. Nat., Mem., vol. 19, pp. 243, 250, 253, 257, 261, 341.
CUSHMAN, J. A.
1925 - Cushman Lab. Foram. Res., Contr., vol. 1, p. 6, pl. 1, fig. 8.
1927a - Jour. Pal., vol. 1. p. 168. pl. 26, figs. 16-17.
1927b - Cushman Lab. Foram. Res., Contr., vol. 3. p. 87.
1948 - Foraminifera: Their classification and economic use. Ed. 4. Cambridge. Mass.: Harvard University Press.