Entolium spedeni Quilty, 1983
QUILTY, P. G. 1983. Bajocian bivalves from Ellsworth Land, Antarctica. New Zealand Journal of Geology and Geophysics, 26 (4): 395-418, figs. 1-60. [p. 401, figs. 12-14]
1983 Entolium (Entolium) spedeni Quilty, 1983
P. G. Quilty, 1983, figures 12-14.
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«MATERIAL: 6 specimens from locality 10, 2 too poorly preserved for accurate identification. All but 1 are internal moulds. Most are slightly distorted. UTGD87352a (holotype), 87275b, 87304b, 87315d, 87338a (all paratypes).
DIAGNOSIS: A large subcircular form with initially strong auricular sulci which die out before reaching margin. Umbo bounded by sulci 75° apart; auricles small.
DESCRIPTION: Shell large, equivalve, approximately equilateral. body of shell subcircular. Length 31-39 mm, height 29-43 mm, thickness not measurable accurately, probably up to 4 mm to the plane of commissure. Umbo bounded at angle of 75º by auricular sulci, 1 of which is slightly more marked than other and corresponding to end with the slightly larger auricle. This end then taken as posterior. Ligament pit tiny, about 1 mm across. Auricular crura not identified. Auricular sulci straight for up to 21 mm, the less prominent being longer by a small margin. Umbo reaches to within 1.5 mm of the hinge line in largest specimen. Hinge line 9 mm long, and umbo 3.5 mm from the anterior end. Anterior and posterior margins make angles of about 140º with ends of hinge line. Anterior margin straight to the anterior point of shell; posterior slightly concave. Anterior extremity notably more dorsal than posterior.
Entire shell surface very smooth, probably shiny in life, marked only seldom by very weak, fine, concentric growth lines. COMPARISON: The species differs from E. cingulatum (Goldfuss) in that the auricular sulci in the Antarctic form die out before reaching the margins,
whereas in E. cingulatum they appear strong to the margin. Entolium fossatum Marwick, recorded by Marwick (1953) as Aratauran, but also extending to the Temaikan, has weaker auricular sulci on both valves and they extend to the margins, whereas in the Antarctic species, they are strong, but die out before reaching the margin. The Antarctic species is significantly larger, and E. fossatum has more prominent and characteristic concentric growth lines. Another New Zealand species is recorded as E. sp. (NZGS6608, ridge crest southeast of Flag Hill summit, S169/f678, Temaikan). Both the new species and E. sp. have the same anterodorsal extremity and similar L/H ratios. They may be the same species, but the Antarctic species is markedly larger. ETYMOLOGY: The species is named for Dr I. G. Speden (New Zealand Geological Survey) who has contributed significantly to the knowledge of New Zealand Mesozoic faunas and who has been of great assistance to me during my studies of the Antarctic Jurassic.
AGE: Middle-Late Bajocian.»
PATRICK GERARD QUILTY, 1983
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