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Alterbidinium punctatum
Holotype. Plate 1, figure 2; GSCA slide no. P51222-02 (¼GSCC slide no. P5205-115G); coordinates 19.8-91.0; EF G56 circle; Nunavut Palaeontology Collection no. NUPB 955; Twosnout creek, Bylot Island. Bylot Island formation.
Etymology. The epithet is an adjectival derivative of the Latin punctum, meaning small hole, dot, spot, in reference to the ornamentation on the pericyst.
Diagnosis. A species of Alterbidinium with a microreticulate to micropunctate endophragm up to 2mm thick. Both the pericyst and endocyst tend to be elongate and are generally separated by a narrow pericoel, although sometimes the two wall layers are in contact. The apical horn is broad, tapering gradually. Some specimens have a clearly delineated, discontinuous pericingulum; in others it is not so obvious, even on the lateral margins. The strong ornamentation tends to obscure the stenodeltaform 2a archaeopyle.
Comments. In one other species of Alterbidinium, Alterbidinium saltanovae, the morphology of the endophragm appears to be similar to that of Alterbidinium punctatum. However, the diagnosis of Alternidinium saltanovae (Vassilyeva in Andreeva-Grigorovich et al. 2011, 47) stated that the endophragm is ‘dense, thick, coarse[ly] granular’. In Alterbidinium punctatum, the endophragm is ‘microreticulate to micropunctate’. We also emphasise this morphological feature in the specific epithet.
Size. Holotype: pericyst length 64mm, pericyst width 38mm, endocyst length 45mm, endocyst width 37mm. Range of five specimens: pericyst length 56–65mm, pericysts width 37– 46mm, endocyst length 41–46mm, endocyst width 36–43mm.
Age. Middle to late Campanian.
Etymology. The epithet is an adjectival derivative of the Latin punctum, meaning small hole, dot, spot, in reference to the ornamentation on the pericyst.
Diagnosis. A species of Alterbidinium with a microreticulate to micropunctate endophragm up to 2mm thick. Both the pericyst and endocyst tend to be elongate and are generally separated by a narrow pericoel, although sometimes the two wall layers are in contact. The apical horn is broad, tapering gradually. Some specimens have a clearly delineated, discontinuous pericingulum; in others it is not so obvious, even on the lateral margins. The strong ornamentation tends to obscure the stenodeltaform 2a archaeopyle.
Comments. In one other species of Alterbidinium, Alterbidinium saltanovae, the morphology of the endophragm appears to be similar to that of Alterbidinium punctatum. However, the diagnosis of Alternidinium saltanovae (Vassilyeva in Andreeva-Grigorovich et al. 2011, 47) stated that the endophragm is ‘dense, thick, coarse[ly] granular’. In Alterbidinium punctatum, the endophragm is ‘microreticulate to micropunctate’. We also emphasise this morphological feature in the specific epithet.
Size. Holotype: pericyst length 64mm, pericyst width 38mm, endocyst length 45mm, endocyst width 37mm. Range of five specimens: pericyst length 56–65mm, pericysts width 37– 46mm, endocyst length 41–46mm, endocyst width 36–43mm.
Age. Middle to late Campanian.