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|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
Rhynchonellata - Athyridida - Meristellidae
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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||The shells are biconvex, subelliptical in outline, the greatest width near the middle, the anterior margin truncate or somewhat produced. Ventral valve rather strongly arched, most convex in the umbonal region from which the surface slopes abruptly to the cardinal margins, and more gently to the sides and front; median portion of the shell depressed in a narrow shallow sinus which is deepest at the front margin, from which it extends two-thirds or more of the distance to the beak; the beak . of the ventral valve is prominent, and strongly incurved over and upon that of the dorsal valve. Dorsal valve slightly less convex than the ventral; highest along the median line, especially on the posterior half of the shell, from which the cardinal slopes are steeper than those over the lateral and antero-Iateral portions; no well defined mesial fold is present but the median portion of the valve is the most prominent from the front to near the beak, which is concealed beneath that of the ventral valve. Surface of both valves marked by lines of growth and by numerous very fine concentric striae, which appear only under a lens.|
|T. W. Amsden 1974||The outline of this species is variable, although all specimens examined are at least slightly elongate; length/width ratio ranges from 1.02 to 1.31 (text-fig. 44; table 11). It has a subequally biconvex profile with a length/thickness ratio ranging from 1.52 to 1.77 (text-fig. 45; table 11). The ventral beak is hooked over the dorsal and in mature individuals may rest directly on the dorsal umbo (pI. 16, fig. 2c). A sulcus begins a few millimeters in front of the ventral beak and extends to the front as a shallow, narrow, indistinct furrow (pI. 16, figs. 2a, 6b, 6c). The dorsal valve commonly has no well-defined fold, although on some shells a slight fold may develop near the front (pI. 16, fig.2d). Both valves are smooth except for growth lines.
The ventral valve has dental plates which in mature individuals are partly buried in the secondarily thickened shell wall (pI. 17, fig.lb). The dorsal hinge plate is divided and rests on the thickened end of the low ridge (pI. 16, figs. 9a-9c). Thejugum is joined and directed posteriorly; the nature of the stem, if any was present, is uncertain.