Chlamys (Plagioctenium) irremotis Olsson & Harbison, 1953
OLSSON, A. A. & A. HARBISON. 1953. Pliocene Mollusca of Southern Florida with special reference to those from North Saint Petersburg. Robert E. Krieger Publishing Company Inc. (1979), p. 1-361, pls. 1-15, 24-48, 57-63. Huntington, N.Y. (Reprint of the Monographs of the Academy of Natural Sciences of Philadelphia, no 8, 1953). [p. 56, pl. 3, figs. 7, 7a]
Shell rather small, about 25 millimeters in height, moderately thin. Valves are subequal, that of the left slightly more convex. In the typical form, the ribs number about 16; these are low, rounded to slightly flattened between interspaces of about the same width. On the right valve the ribs are of uniform size, but on the left each 3rd rib (5 in all) larger than the others, thus giving to this valve a quinquecostate appearance. The ears are large, subequal, flattened, the anterior right bearing a deep byssal notch. Dorso-lateral slopes are narrowly flattened and smooth. Adult shells are generally somewhat worn, hence their surface is smooth but when vvell preserved a fine sculpture of small, raised, lamellose threads is developed and shovvs as a narrow fringe on the sides and corners of the ribs, the summits of the ribs and base of the interspaces remaining smooth.
Height 24 mm., length 22.5 mm., diameter 11.3 mm. The striking characters of this small species are the 5 enlarged ribs of the left valve. In the typical form, of which we have several examples from different localities, the intervals between the 5 primary ribs carry 2 smaller riblets. Specimens from St. Petersburg have usually but one riblet between each primary pair, and the convexity of the valve (with 11 ribs) is somewhat greater than in the typical form; we would have been tempted to consider this form as a subspecies but for the fact that it is associated with other specilnens entirely typical. More material of this species is greatly desired.
Clewiston, Holotype, ANSP 19189.» AXEL ADOLPH OLSSON & ANNE HARBISON, 1953
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A. A. Olsson & A. Harbison, 1953, plate 3.
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