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Dinogymnium avellana
From Fensome et al., 2019:
Dinogymnium avellana (Lejeune-Carpentier, 1951, p.B309; text-fig.3) Evitt et al., 1967, p.16–17. Emendation: Lejeune- Carpentier and Sarjeant, 1983, p.10–11. Holotype: Lejeune-Carpentier, 1951, text-fig.3; Streel et al., 1977, pl.2, fig.7. Originally Gymnodinium (Appendix B), subsequently (and now) Dinogymnium. Boltenhagen (1977, p.76) also proposed this combination. NIA. Age: Maastrichtian.
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Emendation by Lejeune-Carpentier and Sarjeant, 1983:
Emended Diagnosis
Cyst ovoidal, with epitract and hypotract of equal size, having convex flanks. Phragma penetrated by close-set wall canals. Cingulum prominent and nearly equatorial, narrow, moderately deeply impressed and bordered by two ridges, that on its anterior side being more prom inent than that on its posterior side. The cingulum forms only a weak laevorotatory spiral, its two ends differing in antero-posterior position by less than the cingulum's breadth. Sulcus feebly marked on the epitract, more clearly marked on the hypotract and most deeply impressed in its central portion, where there is a deep hollow bordered by slight ridges within the sulcus on both its anterior and posterior sides flagellar marks may be present within this hollow. Numerous longitud inal folds (some 40 in number) extend outward from the cingulum, becoming less prominent or fading out entirely close to the poles. These folds are not uniform, some being more strongly developed than others. Apex and antapex rounded.
Description
As noted by Evitt et al. (1967, p. 17), the holotype is obliquely oriented and, in their terminology, "inflated". Wall-canals certainly are present ; but
we could not determine whether, in addition, any surface granulation was developed. The holotype affords faint suggestion that an apical archaeopyle has begun to develop, but of this we could not be confident.
Remarks
Evitt et al. (1967, p. 17) suggested that th is species, represented as it then was by only a single specimen, might fall with in the range of variation of Dinogymniunm heterocostatum (Deflandre, 1936b) Evitt et al., 1967. However, we cannot accept this conclusion. The smoothly convex ambitus of both epitract and hypotract in D. avellana ; their similarity in shape, with both poles smoothly convex; the more numerous and less well marked longitudinal ridges ; and the lack of the very short secondary ridges all afford differentiating characters. D. avellana is, in many features, more closely comparable with D. acuminatum Evitt et al., 1967, resembling that species in the nature and density of its ribbing ; however, it differs in ambitus, in having a narrower cingulum bordered by less prominent ridges, and in having rounded poles. Nevertheless, it should be stressed that the range of variation of D. avellana remains to be determined. The forms described from Gabon by Boltenhagen (1977) resenble G. avellana in most particulars - and demonstrate the existence elsewhere of rotund forms I However, their cingulum is markedly broader and their longitudinal ribs are even less prominent. A note on orthography :avellana (Gr., hazelnut) is a noun in apposition and thus
should retain an unmodified ending. The variant spelling "avellanum, used by Stover & Evitt (1978) and Lentin & Wiliams (1973, 1981), thus is incorrect.
Dinogymnium avellana (Lejeune-Carpentier, 1951, p.B309; text-fig.3) Evitt et al., 1967, p.16–17. Emendation: Lejeune- Carpentier and Sarjeant, 1983, p.10–11. Holotype: Lejeune-Carpentier, 1951, text-fig.3; Streel et al., 1977, pl.2, fig.7. Originally Gymnodinium (Appendix B), subsequently (and now) Dinogymnium. Boltenhagen (1977, p.76) also proposed this combination. NIA. Age: Maastrichtian.
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Emendation by Lejeune-Carpentier and Sarjeant, 1983:
Emended Diagnosis
Cyst ovoidal, with epitract and hypotract of equal size, having convex flanks. Phragma penetrated by close-set wall canals. Cingulum prominent and nearly equatorial, narrow, moderately deeply impressed and bordered by two ridges, that on its anterior side being more prom inent than that on its posterior side. The cingulum forms only a weak laevorotatory spiral, its two ends differing in antero-posterior position by less than the cingulum's breadth. Sulcus feebly marked on the epitract, more clearly marked on the hypotract and most deeply impressed in its central portion, where there is a deep hollow bordered by slight ridges within the sulcus on both its anterior and posterior sides flagellar marks may be present within this hollow. Numerous longitud inal folds (some 40 in number) extend outward from the cingulum, becoming less prominent or fading out entirely close to the poles. These folds are not uniform, some being more strongly developed than others. Apex and antapex rounded.
Description
As noted by Evitt et al. (1967, p. 17), the holotype is obliquely oriented and, in their terminology, "inflated". Wall-canals certainly are present ; but
we could not determine whether, in addition, any surface granulation was developed. The holotype affords faint suggestion that an apical archaeopyle has begun to develop, but of this we could not be confident.
Remarks
Evitt et al. (1967, p. 17) suggested that th is species, represented as it then was by only a single specimen, might fall with in the range of variation of Dinogymniunm heterocostatum (Deflandre, 1936b) Evitt et al., 1967. However, we cannot accept this conclusion. The smoothly convex ambitus of both epitract and hypotract in D. avellana ; their similarity in shape, with both poles smoothly convex; the more numerous and less well marked longitudinal ridges ; and the lack of the very short secondary ridges all afford differentiating characters. D. avellana is, in many features, more closely comparable with D. acuminatum Evitt et al., 1967, resembling that species in the nature and density of its ribbing ; however, it differs in ambitus, in having a narrower cingulum bordered by less prominent ridges, and in having rounded poles. Nevertheless, it should be stressed that the range of variation of D. avellana remains to be determined. The forms described from Gabon by Boltenhagen (1977) resenble G. avellana in most particulars - and demonstrate the existence elsewhere of rotund forms I However, their cingulum is markedly broader and their longitudinal ribs are even less prominent. A note on orthography :avellana (Gr., hazelnut) is a noun in apposition and thus
should retain an unmodified ending. The variant spelling "avellanum, used by Stover & Evitt (1978) and Lentin & Wiliams (1973, 1981), thus is incorrect.