Lyropecten pyx (Gardner, 1936)
GARDNER, J. 1936. Additions to the molluscan fauna of the Allum Bluff Group of Florida. State of Florida Department of Conservation Geological Bulletin, 14: 7-82, 10 pls. [p. 19, pl. 1, figs. 7-9]
1936 Chlamys (Nodipecten) pyx Gardner, 1936
J. Gardner, 1936, plate 1.
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«Shell of moderate dimensions, rather heavy, inequivalve, inequilateral, obliquely produced posteriorly but not to a marked degree. Right valve more inflated than the left and with a conspicuously different sculpture pattern. Apical angle close to 90º, the ventral margin approximating the quadrant of a circle. Tips of the umbones of both valves sculptured wilh 15 or 16 subequal and equispaced radials. Major ribs usually four in number in the right valve, the two lateral ribs less sharply defined than the two in the middle, each of them including 3 or 4 of the subequal umbonal ribs, which become more or less obscure and sometimes obsolele toward tho margin. Interradials very deep U-shaped channels wilh vertical walls finely grated by the incrementals; a radial threading also developed toward the ventral margin both in the costal and the intercostal areas. Sculpture of the left valve the reverse of that pf the right, the costals high and narrow, representing a single umbonal rib, the intercostals two or three times as wide and rather shallow, in which the intermediate umbonal ribs persist but with no uniformity in prominence; secondary threading developed upon the left valve similar to that upon the right. Intermitent knuckling best developed upon the left valve though there are no hollow bullae as in the typical Nodipecten. Submargins steep wide and smooth wedge-shaped area along the dorsal margin; right posterior auricle with narrow sharper threads 10 in number on the type and a smooth marginal area. Left auricles sharply threaded, the number of radial threads increasing by intercalation to about 10 toward the lateral margin. Ctenolium rather coarse, distinct. Ligament grooves narrow, shallowed and obscured by weathering. Resilial pit small, trigonal. Cardinal crura indicated but not developed with any degree of uniformity. Outline of muscle scars not traceable. Interior of shell rippled in harmony with the mayor external ribbing. Crenae of inner margins reflecting the unbonal ribbing.
Dimensions of cotypes: Right valve, height, 53.5 millimeters; widh, 56.1 millimeters; thickness, 18.5 millimeters. Left valve of another individual, height, 46.4 millimeters; widh, 47.0 millimeters; thickness, 12.5 millimeters. Type material: Two cotypes, a right and left valve not of the same individual, and one juvenil paratype, U. S. Nat. Mus. No. 372894. Type locality: U. S. G. S. Sta. No. 10603, gully south of the road from Eucheeanna to Knox Hill, 6.7 miles south of Argyle, 1.7 miles south east of Eucheeanna, Walton County, Florida. Shoal River formation of the Alum Bluff group. Chlamys (Nodipecten) pyx stands apart from any of the decribed Tertiary or Recent species in the dissimilarity of the sculpture upon the two valves and in the width and prominence of the few ribs upon the right valve. A single imperfect valve, probably a left, from the type locality, but from earlier collection, is apparently N. condylomatus Dall, a Chipola species. Associated with it were juvenils which could not be determined until these later White's Creek collections had been made. Nodipecten pyx, the only other Nodipecten recognized in the Shoal River, is fairly common in the collection No. 10603 and that made from the same locality by the State Geological Survey of Florida. The preservation is not very good, particulary of the adult right valves and much of the sculpture details has been lost. The juveniles, on the other hand, are perfectly preserved. The only species possibility of confusion with any other described species is that of the left juveniles with those of N. condylomatus. The sculpture of the Chipola species is more uniform, and the secondaries are usually grooved medially. Distribution: Shoal River formation, locality 10603e.» JULIA GARDNER, 1936
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«Node 6 separates L. pyx (Gardner, 1936), from members of the tropical Atlantic stem group. This aberrant species was originally described from the Shoal River Formation of Florida, now regarded as late Middle Miocene in age (Jones et al., 1993). It is characterized by a high, trigonal shape, pointed auricles, and unusually well-differentiated key and normal ribs, the latter being very fine relative to the key ribs. Although J. T. Smith (1991a, p. 7) assigned this species to Stralopecten Tucker-Rowland, 1938, studies in progress show that Stralopecten has a later origin and has morphological features that are not shared by Gardner’s species. Aside from its shape, L. pyx resembles other primitive Lyropecten in ribbing pattern.»
WALLER, T. R. 2007. The evolutionary and geographic origins on the endemic Pectinidae (Mollusca: Bivalvia) of the Galapagos Islands. Journal of Paleontology, 81 (5): 929-950 [p. 933]
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Phylogeny of Lyropecten Conrad, 1862 and Nodipecten Dall,
1898; T. R. Waller, 2007, The evolutionary and geographic origins on the endemic Pectinidae of the Galapagos Islands, figure 3. |