Protoscutella mississippiensis (Twitchell, 1915)
Plate: PrMi-10
Series: Eocene Group: Claiborne Formation: Weches
Locale: San Augustine County: San Augustine Stage: Lutetian
Length: 38.3 mm Width: 40.9 mm Height: 5.0 mm
Specimen in photo: NPL 83037 Hypotype
Collector: William R. Thompson, Jr.
University of Texas Non-vertebrate Paleo. Lab.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: USNM 137655 (Originally Johns Hopkins Collection) (Twitchell, 1915; Cooke, 1959).
Locality: USGS 6462, Enterprise, Clarke County, Mississippi.
Stratigraphy: Winona Sand, Claiborne Group.
SYNONYMY
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Neognathostomata Smith, 1981
Order: Clypeasteroida A. Agassiz, 1872
Family: Protoscutellidae Durham, 1955
Genus: PROTOSCUTELLA Stefanini, 1924
Species: Protoscutella mississippiensis (Twitchell, 1915)
TYPE SPECIES: Scutella mississippiensis Twitchell, 1915
DIAGNOSIS
Test variable in size, subcircular to subtriangular, and broader than long. Greatly depressed with a thin margin and a low, central tumid area. The periproct is marginal or slightly inframarginal, situated in a small notch on the posterior border. Distinguished from Periarchus by the marginal position of the periproct (Twitchell, 1915; Cooke, 1959).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Claiborne
Formations: Weches Formation (Texas); Winona Sand, Lisbon Formation (Mississippi/Alabama).
Stratigraphic Units: Paleogene, Middle Eocene (Lutetian).
Counties: San Augustine (Texas); Clarke (Mississippi).
Abundance: Abundant in the Claiborne Group of the Gulf Coastal Plain.
DESCRIPTION
TOP: Length, width, height: 38.3 mm L × 40.9 mm W × 5.0 mm H. Top shape: Subcircular to subtriangular; broader than long (broadest posteriorly). Top domed: Greatly depressed; rises gradually and gently from a thin marginal area to a low, central apex (tumid area).
SIDE: Side shape: Margin thin and faintly undulating; small notch present in the middle of the posterior edge.
BOTTOM: Bottom shape: Flat, except around the peristome where it is slightly concave.
AMB: Amb shape: Petals are elliptical, subequal in length (odd petal slightly longer), and extend about halfway to the margin. Ends are slightly open. Amb arrangement: Ambulacral areas are wider than interambulacral areas at the margin.
PORE PAIRS: Shape: Inner row oval, outer row slit-like. Arrangement: Conjugate. Poriferous zones are rather wide, about equal to the interporiferous areas. A few pairs of pores occur beyond the ends of the petals.
TUBERCLES: Distribution: Surface covered with small uniform tubercles, slightly larger on the underside.
GRANULES: See Tubercles.
FASCIOLE: Absent.
APICAL SYSTEM: Location: Central or subcentral. Plating: Madreporite is relatively large and flush with the surface. Genital pores: Five pores near the edge of the madreporite.
PERIPROCT (ANUS): Shape: Very small and circular. Location: Marginal to slightly inframarginal; situated at the under and inner edge of the notch in the middle of the posterior margin (Twitchell, 1915).
PERISTOME (MOUTH): Shape: Circular. Size: Very small (not over double the size of the periproct). Location: Central or slightly eccentric posteriorly. Features: Ambulacral furrows are simple and straight for 2/3 distance to the margin, then apparently fork symmetrically.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype NPL 83037. Collected by William R. Thompson, Jr.
ETYMOLOGY
Named for the state of Mississippi, where the type specimens were collected in abundance.
REMARKS & COMPARISONS
Remarks: This species is the type species of the genus Protoscutella. It is a key index fossil for the Middle Eocene of the Gulf Coast.
Comparisons:
Plate: PrMi-10
Series: Eocene Group: Claiborne Formation: Weches
Locale: San Augustine County: San Augustine Stage: Lutetian
Length: 38.3 mm Width: 40.9 mm Height: 5.0 mm
Specimen in photo: NPL 83037 Hypotype
Collector: William R. Thompson, Jr.
University of Texas Non-vertebrate Paleo. Lab.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: USNM 137655 (Originally Johns Hopkins Collection) (Twitchell, 1915; Cooke, 1959).
Locality: USGS 6462, Enterprise, Clarke County, Mississippi.
Stratigraphy: Winona Sand, Claiborne Group.
SYNONYMY
- Scutella mississippiensis Twitchell, 1915
- Protoscutella mississippiensis (Twitchell) Stefanini, 1924
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Neognathostomata Smith, 1981
Order: Clypeasteroida A. Agassiz, 1872
Family: Protoscutellidae Durham, 1955
Genus: PROTOSCUTELLA Stefanini, 1924
Species: Protoscutella mississippiensis (Twitchell, 1915)
TYPE SPECIES: Scutella mississippiensis Twitchell, 1915
DIAGNOSIS
Test variable in size, subcircular to subtriangular, and broader than long. Greatly depressed with a thin margin and a low, central tumid area. The periproct is marginal or slightly inframarginal, situated in a small notch on the posterior border. Distinguished from Periarchus by the marginal position of the periproct (Twitchell, 1915; Cooke, 1959).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Claiborne
Formations: Weches Formation (Texas); Winona Sand, Lisbon Formation (Mississippi/Alabama).
Stratigraphic Units: Paleogene, Middle Eocene (Lutetian).
Counties: San Augustine (Texas); Clarke (Mississippi).
Abundance: Abundant in the Claiborne Group of the Gulf Coastal Plain.
DESCRIPTION
TOP: Length, width, height: 38.3 mm L × 40.9 mm W × 5.0 mm H. Top shape: Subcircular to subtriangular; broader than long (broadest posteriorly). Top domed: Greatly depressed; rises gradually and gently from a thin marginal area to a low, central apex (tumid area).
SIDE: Side shape: Margin thin and faintly undulating; small notch present in the middle of the posterior edge.
BOTTOM: Bottom shape: Flat, except around the peristome where it is slightly concave.
AMB: Amb shape: Petals are elliptical, subequal in length (odd petal slightly longer), and extend about halfway to the margin. Ends are slightly open. Amb arrangement: Ambulacral areas are wider than interambulacral areas at the margin.
PORE PAIRS: Shape: Inner row oval, outer row slit-like. Arrangement: Conjugate. Poriferous zones are rather wide, about equal to the interporiferous areas. A few pairs of pores occur beyond the ends of the petals.
TUBERCLES: Distribution: Surface covered with small uniform tubercles, slightly larger on the underside.
GRANULES: See Tubercles.
FASCIOLE: Absent.
APICAL SYSTEM: Location: Central or subcentral. Plating: Madreporite is relatively large and flush with the surface. Genital pores: Five pores near the edge of the madreporite.
PERIPROCT (ANUS): Shape: Very small and circular. Location: Marginal to slightly inframarginal; situated at the under and inner edge of the notch in the middle of the posterior margin (Twitchell, 1915).
PERISTOME (MOUTH): Shape: Circular. Size: Very small (not over double the size of the periproct). Location: Central or slightly eccentric posteriorly. Features: Ambulacral furrows are simple and straight for 2/3 distance to the margin, then apparently fork symmetrically.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype NPL 83037. Collected by William R. Thompson, Jr.
ETYMOLOGY
Named for the state of Mississippi, where the type specimens were collected in abundance.
REMARKS & COMPARISONS
Remarks: This species is the type species of the genus Protoscutella. It is a key index fossil for the Middle Eocene of the Gulf Coast.
Comparisons:
- Periarchus lyelli: P. mississippiensis resembles P. lyelli in general appearance but is readily distinguished by its submarginal/marginal periproct (vs. inframarginal in P. lyelli), greater proportional width, the notch in the posterior edge, and the wider extent of the central tumid area (Twitchell, 1915).
- Protoscutella conradi: P. mississippiensis is very similar but P. conradi (from the Santee Limestone) typically has a more distinct notch and slight variations in petal shape (Cooke, 1959).
- Scutella parma (Recent): Resembles this species but P. mississippiensis has less widely open petals and a less circular form (Twitchell, 1915).
