Zachos—Paleocene echinoids
tract, west of State Highway 263, entrance 2miles north of Butler- LowndesCounty line, LowndesCounty, Alabama (UTMZone 16, E 525,183m,N3,539,105m, NAD83). Clayton Formation, Wade Pit, 0.5mile west of US 27, 1.75 miles south of Stewart-Randolph County line, Randolph County, Georgia (UTM Zone 16, E 707,730m, N 3,531,375m, NAD83). Other localities in New Jersey (Vincentown Fm.) and Alabama, Arkansas, and Georgia (Clayton Fm.) listed by Cooke (1959) and Toulmin (1977).
Remarks.—The description is expanded on the basis of new material from Alabama. Cooke (1959) erected the genus Rho- postoma based on the lack of well-defined petals and the poor development of the phyllodes to distinguish this genus, which he considered to be an echinoneoid, from the cassiduloid genus Trematopygus (= Plagiochasma). Even though d’Orbigny (1853–1856) stated the publication date of his new genus Trematopygus as 1855, Sherwood (1899) reported that the actual publication date was 1858. Melville (1952) pointed out that the name Trematopygus d’Orbigny was preoccupied by Trematopygus Holmgren (an olive fly). However, although the stated publication date of Holmgren’s genus is 1855, the actual publication date seems to be 1858 (Holmgren, 1858). Regard- less, the currently accepted date is 1855 (Hinz, 1985), and Trematopygus d’Orbigny is considered invalid. Plagiochasma, considered a junior synonym of Trematopygus by Lambert and Thiéry (1921), was therefore reinstated by Melville (1952). Cooke (1959) stated that the posterior ocular plates were
not in contact in Rhopostoma ( = Plagiochasma) cruciferum, but this is clearly not the case (Fig. 8.4, 8.5). Smith and Kroh (2011) figured a specimen of Plagio-
chasma cruciferum from the NHM collection (NHM EE4686) reportedly from the Merchantille Formation, Chesapeake and Delaware Canal, St. Georges County, Delaware. The collections made from this canal are from Cretaceous units and the Merchantille Formation is considered to be Campanian in age, not Paleocene (Lauginiger, 1988). No other specimens are known from this locality.
Family uncertain Genus Gitolampas Gauthier, 1889
Gitolampas georgiensis (Twitchell, 1915) Figure 7.3–7.6
1942 Echanthus georgiensis; Cooke, p. 37, pl. 8, figs. 1–3. 1959 Echanthus georgiensis; Cooke, p. 62, pl. 26, figs. 13–16. 1962 Gitolampas georgiensis; Kier, p. 211, text-fig. 172, pl. 40, figs. 3–15.
1915 Echinanthus georgiensis Twitchell, in Clark and Twitchell, p. 139, pl. 65, figs. 1a–d.
Type.—USNM 165683b, from the Clayton Formation, 5 miles south of Ellaville, Schley County, Georgia.
Description.—Medium size, outline subpentagonal, often some- what protruding posteriorly, low to slightly inflated, lower surface concave around peristome, margin rounded. Apical disc mono- basal, four genital pores opening into the proximal ends of the
1013
paired interambulacra; ocular plates small but distinct. Petals long and narrow, anterior pair diverge at 140º, posterior pair diverge at 60º. Petals extend nearly tomargin, open distally; pores circular to elliptical, conjugate, oblique in midsection; interporiferous zones up to twice as wide as poriferous zones; pores single beyond petals, one pore per ambulacral plate orally, restricted to adradiad sutures except in floscelle. Peristome anterior, pentagonal, nearly equant; phyllodeswell developed, one, sometimes two sphaeridial pits, bourrelets slightly inflated. Periproct marginal, enclosed between 5th pair of post-basicoronal plates below the ambitus and the 6th pair above (obscured by plate fractures in Fig. 7.6), vertical, taller than wide, indents posterior margin. Aboral and marginal surface covered in small, sunken tubercles interspersed with fine granules; tubercles larger on oral surface, increasing in size and decreasing in density towards peristome, but denser and smaller within area of the floscelle, fading into granules on the bourrelets; narrow, naked sternal area.
Additional material.—MMNS5299, from the Clayton Formation, Resource Management Services Palmyra tract, Lowndes County, Alabama.
Occurrence.—Clayton Formation, Dr. A.J. Parkes farm, 5 miles south of Ellaville, Schley County, Georgia (exact location unknown). Clayton Formation (McBryde Member), Resource Management Services Palmyra tract, west of State Highway 263, 2 miles north of Butler-Lowndes County line, Lowndes County, Alabama (UTM Zone 16, E 525,183m, N 3,539,105m, NAD83). Cedar Creek, either side of State Highway 263, 6 miles northwest of Greenville, Butler County, Alabama (UTM Zone 16, E 529,209m, N 3,531,611m, NAD83). Other localities in Alabama listed by Cooke (1959) and Toulmin (1977).
Remarks.—The description is expanded based on new material
fromAlabama.Cooke (1959) placed ?Cassidulus (Galerolampas) fontis Cooke (1959) in synonymy with this species, but the type of C. fontis has better developed bourrelets and a transverse peristome (with no evidence of the crushing of the periproctal region described by Cooke). The type of C. fontis (USNM 498997) was recovered from well washings originating from an unknown depth and formation. It was included in a larger lot of fossils, the remainder of which are now unfortunately lost. Cooke (1959) described the type ofG. georgiensis(USNM165683b) as a siliceous pseudomorph. The specimen is actually recrystallized calcite,though eroded onthe aboral
surface.Manyof the
1977 Gitolampas georgiensis; Toulmin, p. 178, pl. 9, figs. 14–16. 2000 Gitolampas georgiensis; Smith and Jeffery, p. 227.
specimens fromthe vicinity of Luverne,Alabama (some collected from now abandoned shallow open pit iron mines) are internal molds composed of hematite. A few specimens are beautiful replacements of the original calcite test with hematite. Gitolampas georgiensis is one of the most common echinoids found in the Clayton Formation in Alabama.
Order Holasteroida Durham and Melville, 1957 Family Holasteridae Pictet, 1857
Subfamily Pseudholasterinae Smith and Jeffery, 2000 Genus Pseudholaster Pomel, 1883
Pseudholaster cinctus (Morton, 1830a) Figure 7.7, 7.8
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