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1018


Journal of Paleontology 91(5):1001–1024


species is assigned to Diplodetus. A steinkern attributable to D. americanus (MMNS 5336) was collected from the Prairie Bluff Chalk at Prairie Bluff, Wilcox County, Alabama (UTM Zone 16, E 462,056 m, N 3,555,388 m, NAD83) and D. americanus is known from other Prairie Bluff Chalk localities in Mississippi, and is also reported from the Coon Creek Member of the Ripley Formation (Maastrichtian) in Tennessee (Ciampaglio and Phillips, 2016).


Family Schizasteridae Lambert, 1905 Genus Linthia Desor, 1853


Linthia alabamensis Clark, 1915 Figures 9.5, 9.7–9.9, 11.1–11.4, 13.1


1915 Linthia alabamensis Clark in Clark and Twitchell, p. 153, pl. 71, figs. 1a–d, 2a–d.


1933 Linthia maverickensis Gardner, p. 110, pl. 4, figs. 13, 14. 1942 Schizaster (Linthia) alabamensis; Cooke, p. 42. 1959 Linthia alabamensis; Cooke, p. 69, pl. 29, figs. 5–7. 1977 Linthia alabamensis; Toulmin, p. 178, pl. 9, fig. 5–7.


Type.—Holotype USNM137371, from the Clayton Formation, Prairie Creek, Wilcox County, Alabama. Holotype of Linthia maverickensis USNM 370904.


Description.—Small to medium size, subcircular, wider than long, indented anteriorly and posteriorly; fairly tall, apex behind apical disc, oral surface flat and unkeeled, margins rounded. Apical disc ethmolytic, four genital pores, lateral pairs distinctly closer; plating variable but genital plate 4 usually occluded from genital 2 by posterior elongation of genital 3 (Fig. 11.1–11.3), sometimes not (Fig. 11.4). Ocular III deeply inserted, inter- ambulacral plates 2b and 3a occluded from ocular by ambulacral plates. Anterior ambulacrum depressed, shallowly near apical disc, but sulcus deepens towards anteriormargin, then shallows to peristome; uniserial series of pore pairs, outer pores larger than inner, separated by single tubercle proximal to the ocular, tubercles lacking distally, very slightly oblique. Anterior petals straight to slightly flexed, diverge at 120º–130º,somewhat wider in small (juvenile) specimens, posterior petals straight, about 80 percent length of anterior, diverge at 60º; interporiferous zones about as wide as poriferous, pores conjugate, elongate and unequal, outer pores larger. Periproct marginal, sloping forward and visible from above, taller than wide. Peristome reniform, lipped, in anterior quarter of test; labrum short, contacts sternal plates. Peripetalous fasciole deeply indented, parallels anterior petals for about three quarters of their length. Lateral fasciole branches near tips of anterior petals without offset. Tubercles small and densely spaced aborally, larger alongmargin of anterior ambulacrum; larger and less dense orally, with asymmetric areoles, posterior ambulacra naked.


Additional material.—MMNS 4504, Clayton Formation, Rock- port, Hot Spring County, Arkansas, MMNS 7164, Clayton For- mation, Palmyra tract, LowndesCounty, Alabama,MMNS7354, Clayton Formation, Possum Grape, Jackson County, Arkansas, NPL 4623, Kincaid Formation (Tehuacana Limestone), Kosse, Limestone County, Texas, UF 278479, UF 278480, UF 278481, Clayton Formation,Mussel Creek, Lowndes County, Alabama.


Figure 11. Linthia alabamensis Clark, 1915, apical disc plate patterns: (1) MMNS 7354, from the Clayton Formation, Possum Grape, Jackson County, AR; (2) UF278479, from the Pine Barren Member, Clayton Formation, Mussel Creek, Lowndes County, AL; (3) UF278480, from the Pine Barren Member, Clayton Formation, Mussel Creek, Lowndes County, AL; (4) UF278481, from the Pine Barren Member, Clayton Formation, Mussel Creek, Lowndes County, AL. Scale bars are 0.5mm.


Occurrence.—Clayton Formation, Prairie Creek, Wilcox County, Alabama (exact locality unknown). Kincaid Formation, Indio Ranch, Maverick County, Texas (exact locality unknown) (Type of L. maverickensis). Clayton Formation (McBryde Member), Resource Management Services Palmyra tract, west of State Highway 263, Butler and Lowndes County, Alabama (UTMZone 16, E 525,183m, N 3,539,105m, NAD83). Clayton Formation (Pine Barren Member), Knights Road at Mussel Creek, Lowndes County, Alabama (UTMZone 16, E 527,935 m, N 3,537,270 m, NAD83). Clayton Formation, beside Walmart, Rockport, Hot Spring County, Arkansas (UTM Zone 15, E 515,466 m, N 3,805,319 m, NAD83). Clayton Formation, Possum Grape, Jackson County, Arkansas (exact locality unknown). Clayton Formation, South Tippah Creek, west of State Highway 15, 1.75 miles north of Blue Mountain, Tippah County, Mississippi (UTM Zone 16, E 316,260m, N 3,841,071m, NAD83). Clayton Formation, excavations on State Highway 15, south of Ecru, Pontotoc County,Mississippi (UTM Zone 16, E 312,726m, N 3,798,184m, NAD83); Kincaid Formation (TehuacanaLimestone), quarry east side ofCountyRd 248, 0.5 mile south of State Highway 7, 5.25 miles west of Kosse, Falls County, Texas (UTM Zone 14, E 717,062 m, N 3,465,022 m, NAD83). Kincaid Formation (Tehuacana Limestone), pit south of State Highway 7, ~12 miles east of Marlin, Falls County, Texas (UTM Zone 14, E 686,125m, N 3,463,140m, NAD83). Wills Point Formation, left bank of Dry Creek at confluence with Colorado River, 3 miles below Travis-Bastrop County line, Bastrop County, TX UTMZone 14, E 647,011 m, N 3,340,004 m, NAD83). Other localities in Alabama and Arkansas (Clayton Formation) listed by (Cooke, 1959) and (Toulmin, 1977).


Remarks.—Description is expanded based on new material from Alabama, Arkansas, and Texas. The unequal lengths of the anterior and posterior petals (the posterior petals have an average plate count ~74% that of the anterior petals) suggests


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