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Sivorthis tenuicostatus
Taxonomy
Orthambonites tenuicostatus was named by Cooper (1956). Its type specimen is USNM 116875b, a shell, and it is a 3D body fossil.
It was recombined as Sivorthis tenuicostata by Jaanusson and Bassett (1993); it was recombined as Sivorthis tenuicostatus by Candela and Harper (2014).
It was recombined as Sivorthis tenuicostata by Jaanusson and Bassett (1993); it was recombined as Sivorthis tenuicostatus by Candela and Harper (2014).
Synonymy list
| Year | Name and author |
|---|---|
| 1956 | Orthambonites tenuicostatus Cooper pp. 314 - 315 figs. Plate 38, E, figures 30-40 |
| 1962 | Orthambonites tenuicostatus Williams pp. 99 - 100 figs. Pl. VIII, figs. 9-11 |
| 1993 | Sivorthis tenuicostata Jaanusson and Bassett |
| 2014 | Sivorthis tenuicostatus Candela and Harper p. SI |
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If no rank is listed, the taxon is considered an unranked clade in modern classifications. Ranks may be repeated or presented in the wrong order because authors working on different parts of the classification may disagree about how to rank taxa.
†Sivorthis tenuicostatus Cooper 1956
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Diagnosis
| Reference | Diagnosis | |
|---|---|---|
| G. A. Cooper 1956 | Shell small for the genus, wider than long, subrectangular in outline; hinge narrower than the greatest shell width which is at the middle; sides nearly straight or very gently rounded ; anterior margin broadly rounded ; surface marked by 34 to 40 elevated and narrowly rounded costae separated by spaces equal to or slightly wider than the costae ; costae appearing in 2 generations, one at the beak and the other on the anterior slope of the umbo.
Pedicle valve strongly convex in lateral profile ; greatest depth at about the middle; anterior profile swollen in the middle and with moderately long and gently convex, fairly steep, lateral slopes. Umbo swollen and beak incurved ; median region inflated to form an inconspicuous fold ; anterior slope steep ; lateral slopes gently inflated ; umbonal slopes steep. Interarea moderately long, apsacline. Interior with small teeth, short, thick dental plates ; umbonal cavities filled with shell material ; delthyrial cavity deep ; floor of muscle area slightly thickened anteriorly ; vascula media and median ridge not developed. Brachial valve gently convex in lateral profile ; greatest depth located in the posterior third ; anterior profile broadly convex and gently indented in the median area ; sulcus originating at the umbo, widening to the anterior margin where it occupies slightly less than 2 mm, Flanks bounding sulcus gently inflated ; umbonal slopes short and fairly steep; posterolateral extremities somewhat flattened. Interior with narrow, shallow notothyrial cavity, but thickened notothyrial platform ; cardinal process a low ridge, not well developed ; median ridge poorly defined, extending to about the middle ; brachial process short and stout. | |
| A. Williams 1962 | Subrectangular Orthambonites with a strongly convex pedicle valve over three-quarters as wide as long and a gently convex, sulcate brachial valve; costellate ornamentation consisting of about 32 angular ribs numbering 2 or 3 per millimetre antero-medianly and including 15 costae and one generation of costellae arising externally and internally on the pedicle valve; ventral muscle-scar subquadrate, about one-quarter the length of the valve. |