Pecten (Plagioctenium) evergladensis Mansfield, 1932
MANSFIELD, W. C. 1932. Pliocene fossils from limestone in Southern Florida. United States Geological Survey Professional Paper, 170-D: 43-56, pls. 14-18. [p. 47, pl. 17, figs. 1, 2, 4, 5]
«Pecten (Plagioctenium) evergladensis Mansfield, n. sp.
Plate 17, Figures 1, 2, 4, 5 Shell small, broadly orbicular, probably nearly equivalve, inequilateral, the posterior region being more produced. Right valve of holotype inflated and swollen behind the umbo; posterior region more gently sloping to submargins than anterior; base broadly rounded. Sculptured with 22 nearly flat laterally sloping ribs separated by much narrower interspaces. Sides of ribs and submargins of shell marked with moderately coarse, nearly erect, concentric lamellae. Submargins without any distinct radials. Right ear with a shallow byssal notch and ornamented with six radials; left ear bearing weak radials on the lower half. Left valve of immature and slightly corroded paratype sculptured with 20 ribs, which are a little lower than those on right valve; submargins without distinct radials.
Dimensions: Holotype, right valve (catalogue No. 371323, U. S. Nat. Mus.), length, 58 millimeters; height, 52 millimeters. Paratype, left valve (catalogue No. 371324, U. S. Nat. Mus.), length, 29 millimeters; height, 28 millimeters. Type locality: Station 1/1178, Tamiami Trail, 6 miles west of crossroad leading to Everglades, Collier County. The new species differs from Pecten gibbus gibbus Linnaeus in the absence of any distinct radials on the submargins and in having a much more inequilateral shell. In the latter feature it more closely resembles Pecten circularis Sowerby, a Recent species geographically ranging on the west coast from Monterey, Calif., to the Gulf of California and Paita, Peru. Pecten (Plagioctenium) comparilis Tuomey and Holmes, an upper Miocene species, appears to be the ancestral form of the new species. Pecten mendenhalli Arnold, a Pliocene species collected at Santa Rosalia, Lower California, and also occurring at Alverson Canyon, San Diego County, Calif., is nearly related to the new species. Occurrence: Pliocene. Station 1/1178 (type locality, 2 valves), station 1/1177 (paratype locality, 3 valves), station 1/1180 (5 valves), station 1/1176 (2 valves), 1/1179 (4 valves). Specimens occurring in the Caloosahatchee marl, Florida, have the same characteristics as the new species and appear to belong to it. The Caloosahatchee specimens appear to have been referred to P. gibbus gibbus Linnaeus by Dall, [19] but they are unlike the Recent species referred to that variety.» [19] Dall. W. H., Contributions to the Tertiary fanna of Florida: Wagner Free lnst. Sci. Trans., vol. 3, pt. 4. p. 745, 1898.
WENDELL CLAY MANSFIELD, 1932
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W. C. Mansfield, 1932, plate 17.
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