Catalog - Heterohelix dentata

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Heterohelix dentata

Citation: Heterohelix dentata Stenestad 1968

Type specimens: PI. 1, fig. 3, 4, 5, 6, 8, 9, 11, PI. 2 fig. 1, 2, 3.

Type age (chronostrat): Maastrichtian

Type locality: from outcrop "Dania" near Mariager

Type repository: Copenhagen, Denmark

Test with initial small-sized planispiral coil or more often biserial throughout. Chambers reniform increase rapidly in size as added. Sutures distinct, depressed and curced. Test compressed with subangular to angular periphery. No peripheral structures present. Test wall smooth, finely perforated. Scattered pustules can be recorded on the earlier formed chambers, the last formed ones being invariably smooth. Aperture a moderate high arch at the base of the apertural face is bordered by thin flanges.

Size of holotype: Length: 0.323 mm; breadth: 0.243 mm; thickness: 0.115 mm. 14 chambers.

Remarks: The slightly reniform adult chambers give the test a resemblance to H. pulchra (BROTZEN), from which it differs in the less compressed test and the low initial chambers with the somewhat roughened surface and the slightly depressed to flush or even slightly limbate sutures. The cross section of the adult chambers is not circular as in H. pulchra, and the shape changes from the aperture to the periphery. This special shape of the peripheral part of the adult chambers and the dentate margin are never seen in H. pulchra.

H. dentata differs from H. glabrans (CUSHMAN), which is also present in Danish deposits, in the shape of the adult chambers and in the cross section of the adult margin which is broadly rounded and never subacute as by H. glabrans.

H. dentata is morphologically related to H. planata (CUSHMAN) which in the Upper Campanian and the lowermost Maestrichtian produces some specimens with adult chambers not very unlike those of H. dentata (see Plate 1 fig. 10). An examination of hypotypes from KEMP CLAY, Texas, has shown that typical specimens of H. glabrans (CUSHMAN) are present in the Danish Upper Maestrichtian. The specimen figured in plate 1 fig. 7 is morphologically very close to H. dentata, but has an atypical last chamber resembling those of H. glabrans. H. dentata is, so to speak, a morphologic transitional form between H. planata and H. glabrans.

Distribution: Upper Maestrichtian in "Dania" by Manager, Fristrup (North Jutland), Højerup (Stevns), Storebælt (borehole G.I. no. 21); Lower Maestrichtian in the Batum area (borehole 16A and outcrop "Skandia") and in the Ålborg area (at most localities, such as "Norden", "Danmark", "Rørdal" etc.) (White Chalk facies).

Stratigraphic range: Upper part of Lower Maestrichtian to the lower Danian boundary.

Material: About 200 specimens from Upper and Lower Maestrichtian in the Danish Embayment.

References:

Stenestad, E. (1968). Three new species of Heterohelix Ehrenberg from the upper Senonian of Denmark. Meddelelser fra Dansk Geologisk Forening. 18(1): 64-70. gs

CATALOG OF ORIGINAL DESCRIPTIONS: Heterohelix dentata Stenestad 1968

Heterohelix dentata

References:

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