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|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Rhynchonellata - Orthida - Plaesiomyidae
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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.
|G. A. Cooper 1956||Like all species of Multicostella this one is also very variable in size and certain of the details of the surface. The type specimen (G.S.C. 1034) which is preserved in the Geological Survey of Canada collection is a fairly large specimen but is poorly preserved. Much of the exterior has been stripped from the shell, making it impossible to determine the details of the costellae exactly. The convexity of both valves is low and at the front of the pedicle valve the specimen is depressed to form a broad and shallow sulcus. The sulcus of the brachial valve is shallow and narrow and extends about to the middle of the valve. At the front of the brachial valve a low swelling corresponds to the sulcus of the pedicle valve. Some specimens show a clearly defined sulcus in the brachial valve extending from the beak to the anterior margin. Ten costellae may be counted in a distance of 5 mm. at the front margin of the holotype. Inasmuch as this specimen is much exfoliated, it is possible that the finest costellae of the latest generation are lost and cannot be counted. The holotype is 18.5 mm. long, 21 mm. wide, and 5.5 mm. thick. Specimens preserving the exterior show the costellae to be narrow, elevated, and bundled with ones of various sizes in several generations.|