"Pecten" howei mariannensis Glawe, 1969
GLAWE, L. N. 1969. Pecten perplanus stock (Oligocene) of the Southeastern United States. Geological Survey of Alabama Bulletin, 91: 1-179, pls. 1-5. [p. 57, pl. 4, figs. 1, 2, 4, 5; pl. 5, figs. 2-4]
1969 Pecten howei mariannensis Glawe, 1969
L. N. Glawe, 1969, plates 4, 5.
|
«Pecten (Pecten) poulsoni Morton. Dall, 1898, Wagner Free Inst. Sci., Philadeiphia, Trans., v. 3, part 4, p. 719 (part?).
Pecten (Pecten) poulsoni Morton. Tucker-Rowland, 1936, Am. Mid. Naturalist, v, 17, p. 476 (part?). Pecten poulsoni. MacNeil, 1944, Am. Assoc. Petrol. Geologists Bull., v. 28, no. 9, p. 1324, bed 5. Pecten (Pecten) poulsoni Morton. Delaney, 1963, Jour. Paleontology, v. 37, p. 1267 (part), pl. 178, fig. 13. MATERIAL: Holotype (Louisiana State University Geology Museum no. 8076, right valve): height 32.8 mm, length 34.0 mm, hinge length 20.3 mm, inflation 7.8 mm; morphotype D, 17 ribs. Paratype (Louisiana State University Geology Museum no. 8077, left valve): height 30.6 mm, length 31.5 mm, hinge length 18.4 mm, inflation 5.0 mm; morphotype D, 19 ribs. Holotype and paratype are from bed 03 at Smith quarries near Marianna, Florida (section 18). In addition to the types, a total of 82 left valves and 36 right valves are here referred to this subspecies. For descriptive data for each individual, see appendix D.
DIAGNOSIS: Pecten howei having individuals with widely spaced concentric lamellae as the dominant form. DESCRIPTION: Shell orbicular, of medium thickness; small to medium-sized, maximum height 41.2 mm (mean height 25.4 mm), maximum length 42.6 mm (mean length 26.0 mm); unequally biconvex, the right valve moderately convex (mean I:H = 0.22), the left slightly less convex (mean I:H = 0.14); hinge line slightly concave in right valve, nearly straight in left valve; ribs low, rounded, and generally with a radial lira; ribs slightly wider than interspaces; right valve with 17 to 20 ribs (mean 18.m and left valve with 17 to 21 ribs (mean 18.7); concentric lamellae closely or widely spaced, the widely spaced form (morphotype D) dominant. Ears fairly large, nearly equal, and nonstriated except for 1-5 fortuitous threads on some specimens; byssal notch shallow, lacking ctenolium. Hinge with provinculum, two pairs of cardinal crura, occasionally a rudimentary third pair, and one pair of auricular crura terminating distally at a strong, rounded, oblong ridge; resilial pit medium-sized, fringed with lateral ridges in the right valve. Add uctor muscle scars large; interior of valves with distinct internal ribs fluted along the ventral margin. VARIATION: Populations of P. howei mariannensis consist of morphotypes A, D, and E, the proportion of D being 50 percent or greater (see figs. 15 and 16). This subspecies has low variability in morphological characters between different samples. OCCURRENCE: Marianna and Suwannee Limestones of panhandle Florida. Glendon and Byram Formations of south-central Alabama and sparsely as far west as Sylvarena, Mississippi (locality 04). LOCALITIES: Samples 01, 02, and 03 at near Marianna, Fla. (section 18); sample 00 at Natural Bridge, Fla. (composite section 15); samples 00 and 01 at Harts Bridge, Ala. (section 14); samples 00 and 01 at McGowin's Bridge (section 13); sample 01 at Castleberry, Ala. (composite section 12); samples 08 and 09 at St. Stephens, Ala. (section 08); sample 06 at Millry, Ala. (composite section 07); sample 04 at Waynesboro, Miss. (composite section 06); and sample 04 at Sylvarena, Miss. (composite section 04). For additional localities, see catalogue of references. AFFINITIES: P. howei mariannensis is intermediate in the chronologic series from P. perplanus perplanus to P. howei howei and includes populations consisting of morphotypes A, D, and E, with D the dominant form. P. perplanus perplanus populations are dominated by morphotype A, and P. howei howei populations by morphotype E. Comparisons between various characters of these taxa are shown in table 8.» LLOYD N. GLAWE, 1969
|