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|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Rhynchonellata - Athyridida - Rhynchospirinidae
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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.
|T. E. Savage 1913||Shell biconvex, subovate in outline, somewhat longer than wide. Ventral valve more convex than the dorsal, the greatest convexity in the umbonal region from which the surface slopes rather steeply to the cardinal and cardino-Iateral margins, and more gently to the' sides an,d front; the mesial portion of the valve somewhat elevated, with a prominent stria on each side of the median line; in the furrow between these striae is a rounded ridge which extends nearly three-fourths of the distance from the front to the beak. The beak is prominent and pointed, but not much incurved over the hinge line. Dorsal valve moderately convex, the greatest depth a little posterior to the middle, from which the surface slopes with a rather uniform curvature to the cardinal, lateral and anterior margins; the mesial portion of the valve bears a slight depression which is occupied by a low ridge extending nearly to the beak and is divided by a shallow furrow in the anterior half of its length, with a trace of an additional division near the front margin. The beak is small and closely in curved beneath that of the ventral valve. Surface of both valves marked by radiating striae of which about four on each side of the median line of the valves extend to the beaks; of these, the two adjacent to the median line on each valve usually divide twice, while some of the others divide once and others divide twice between the beak and the margin. No distinct concentric lines of growth are visible.|