Latibrachythyris cf. crassa (De Koninck, 1843)
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publication ID |
https://doi.org/ 10.4202/app.00972.2022 |
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persistent identifier |
https://treatment.plazi.org/id/41708783-FFF0-FF92-8F34-CEF6FD7CFD83 |
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treatment provided by |
Felipe |
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scientific name |
Latibrachythyris cf. crassa (De Koninck, 1843) |
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Latibrachythyris cf. crassa (De Koninck, 1843)
Figs. 14T–V View Fig , 16A View Fig .
Material.—Six ventral valves: MPUM12038 (RCC1-21); MPUM12039 (RCC1-34a); MPUM12040 (RCC54-10a); MPUM12041 (RCC54-17a); MPUM12042 (RCC1- 15a; RCC48-7). Five fragments: MPUM12087 (RCC1-8b, 17b; RCC8-3b; RCC39-7; RCK15-38). All from mud mound complex of Ricklow Quarry, Monyash, Derbyshire, UK, Monsal Dale Limestone Formation, Brigantian, upper Visean.
Description.—Medium-sized shell with transversely subrectangular outline; cardinal margin straight, almost as wide as the maximum width. Cardinal angles obtuse; cardinal extremities subangular. Anterior commissure uniplicate. Ventral valve strongly convex. Ventral interarea low, apsacline, weakly denticulate. Sulcus starting as a furrow from umbo, becoming wider and broadly rounded anteriorly.
Ornamentation consists of low costae, almost flat, with narrow interspaces. At a variable distance from the umbo, commonly less than 10.0 mm, costae start to irregularly bifurcate giving rise to a distinctive pattern of ribs of variable width. Lateral ribs number four per 5.0 mm width at 2.2 mm from the umbo, six to seven at 30.0 mm. Sulcus ornamented by four ribs at 10.0 mm from the umbo, 16 ribs at 30.0 mm from the umbo. Micro-ornamentation of faint regularly concentric growth lines; sporadic lamellae.
Specimens with a length of approximately 25.0 mm have a less convex profile, with flatter lateral slopes, with respect to larger adult shells, which have steep, rounded lateral slopes resulting in a strongly convex shell with the maximum width at shell mid-length.
Remarks.—The specimens are similar to Latibrachythyris crassa for their convex valves with steep lateral slopes, moderate sulcus and fold and ornamentation. They differ from L. pinguis and L. rotundatus ( Sowerby, 1825) in having a finer radial ornamentation of bifurcating ribs.
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