Orthopsis planulata Clark, 1915
Plate: OrPl-10
Series: Upper Cretaceous Group: Washita Formation: Main Street
Locale: Denison County: Grayson Stage: Lower Cenomanian
Length: 32.9 mm (largest) Height: 13.8 mm (estimate)
Specimen in photos: U.S.N.M. 103708 and 103708A Holotypes
Collector: USGS SURVEY
Repository: Paleobiology Dept., NMNH, Smithsonian Institution
Plate: OrPl-20
Series: Upper Cretaceous Group: Washita Formation: Weno
Locale xxxxxxx County: xxxxxx Stage: Lower Cenomanian
Length: 25.1mm Height: estimate 12 Top of test missing
Collector: Lance Southwick
HOLOTYPE INFO:
Syntypes: USNM 103708 and 103708A (Two specimens on a single block) (Clark & Twitchell, 1915).
Locality: Denison, Grayson County, Texas.
Stratigraphy: "Grayson marl member of the Denison formation" (Clark, 1915); likely Main Street or Grayson Formation.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Echinacea Claus, 1876
Order: Orthopsida Mortensen, 1942
Family: Orthopsidae Duncan, 1889
Genus: ORTHOPSIS Cotteau, 1864
Species: Orthopsis planulata Clark, 1915
TYPE SPECIES: Cidaris miliaris d'Archiac, 1835
DIAGNOSIS
Test small, depressed, and circular in ambital outline. Distinguished by a distinctly flattened upper surface (planulate) and concave lower surface. Interambulacral tubercles are much reduced on the upper surface compared to the lower surface. Smaller, less elevated, and less pentagonal than O. occidentalis (Adkins, 1928).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Main Street Limestone; Grayson Marl, Weno
Stratigraphic Units: Upper Cretaceous, Albian/Cenomanian.
Counties: Grayson.
Abundance: Rare; known from the type slab and one other.
DESCRIPTION
TOP: Length, width, height: W 32.9 mm × H13.8 mm.
Top shape: Circular in ambital outline (Clark & Twitchell, 1915).
Top domed: Upper surface distinctly flat ("planulate"), except directly at the apical system, which is slightly elevated.
SIDE: Side shape: Much depressed; less elevated than O. occidentalis (Adkins, 1928).
BOTTOM: Bottom shape: Lower surface concave (Clark & Twitchell, 1915).
AMB: Amb shape: Narrow.
Amb arrangement: Two rows of small tubercles that become indistinct toward the apical system.
Plating: Plates are simple primaries on the upper surface. From just above the ambitus to the peristome, plates are compound (two primaries commonly combine, with the suture passing through the interporiferous tubercle) (Clark & Twitchell, 1915).
PORE PAIRS: Arrangement: Straight uniserial series.
TUBERCLES: Primary Perforated: Yes.
Primary Crenulate: No (Uncrenulated) (Clark & Twitchell, 1915).
Interambulacral Tubercles: Broad area with six rows of tubercles on the under surface; these are much reduced on the upper surface.
Ambulacral Tubercles: Small.
GRANULES: (Not specified).
FASCIOLE: Absent in Orthopsidae.
APICAL SYSTEM: Location: Slightly elevated.
PERIPROCT (ANUS): Not described.
PERISTOME (MOUTH): Size: Moderate size (Clark & Twitchell, 1915).
SPINES: Condition: Several spines preserved in the matrix of the adoral surface (Clark & Twitchell, 1915).
SPECIMENS STUDIED & CONDITION: Syntypes USNM 103708 and 103708A. Two specimens embedded in a single mass of indurated marl; one shows the adoral surface, the other the aboral surface.
ETYMOLOGY
From the Latin planulata (flat or level), referring to the distinctly flattened upper surface.
REMARKS & COMPARISONS
Remarks: Lambert (1914), in a review of Clark's monograph, noted that O. planulata seems difficult to distinguish from O. occidentalis (Cragin), suggesting a close relationship or potential synonymy. However, Adkins (1928) maintained it as a distinct species, noting it is "smaller, less elevated, and less pentagonal" than O. occidentalis.
Comparisons:
Remarks: (02-2026) A specimen was found in the xxxx formation in xxxxx County by Lance Southwick, of xxxxxx,
Plate: OrPl-10
Series: Upper Cretaceous Group: Washita Formation: Main Street
Locale: Denison County: Grayson Stage: Lower Cenomanian
Length: 32.9 mm (largest) Height: 13.8 mm (estimate)
Specimen in photos: U.S.N.M. 103708 and 103708A Holotypes
Collector: USGS SURVEY
Repository: Paleobiology Dept., NMNH, Smithsonian Institution
Plate: OrPl-20
Series: Upper Cretaceous Group: Washita Formation: Weno
Locale xxxxxxx County: xxxxxx Stage: Lower Cenomanian
Length: 25.1mm Height: estimate 12 Top of test missing
Collector: Lance Southwick
HOLOTYPE INFO:
Syntypes: USNM 103708 and 103708A (Two specimens on a single block) (Clark & Twitchell, 1915).
Locality: Denison, Grayson County, Texas.
Stratigraphy: "Grayson marl member of the Denison formation" (Clark, 1915); likely Main Street or Grayson Formation.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Echinacea Claus, 1876
Order: Orthopsida Mortensen, 1942
Family: Orthopsidae Duncan, 1889
Genus: ORTHOPSIS Cotteau, 1864
Species: Orthopsis planulata Clark, 1915
TYPE SPECIES: Cidaris miliaris d'Archiac, 1835
DIAGNOSIS
Test small, depressed, and circular in ambital outline. Distinguished by a distinctly flattened upper surface (planulate) and concave lower surface. Interambulacral tubercles are much reduced on the upper surface compared to the lower surface. Smaller, less elevated, and less pentagonal than O. occidentalis (Adkins, 1928).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Main Street Limestone; Grayson Marl, Weno
Stratigraphic Units: Upper Cretaceous, Albian/Cenomanian.
Counties: Grayson.
Abundance: Rare; known from the type slab and one other.
DESCRIPTION
TOP: Length, width, height: W 32.9 mm × H13.8 mm.
Top shape: Circular in ambital outline (Clark & Twitchell, 1915).
Top domed: Upper surface distinctly flat ("planulate"), except directly at the apical system, which is slightly elevated.
SIDE: Side shape: Much depressed; less elevated than O. occidentalis (Adkins, 1928).
BOTTOM: Bottom shape: Lower surface concave (Clark & Twitchell, 1915).
AMB: Amb shape: Narrow.
Amb arrangement: Two rows of small tubercles that become indistinct toward the apical system.
Plating: Plates are simple primaries on the upper surface. From just above the ambitus to the peristome, plates are compound (two primaries commonly combine, with the suture passing through the interporiferous tubercle) (Clark & Twitchell, 1915).
PORE PAIRS: Arrangement: Straight uniserial series.
TUBERCLES: Primary Perforated: Yes.
Primary Crenulate: No (Uncrenulated) (Clark & Twitchell, 1915).
Interambulacral Tubercles: Broad area with six rows of tubercles on the under surface; these are much reduced on the upper surface.
Ambulacral Tubercles: Small.
GRANULES: (Not specified).
FASCIOLE: Absent in Orthopsidae.
APICAL SYSTEM: Location: Slightly elevated.
PERIPROCT (ANUS): Not described.
PERISTOME (MOUTH): Size: Moderate size (Clark & Twitchell, 1915).
SPINES: Condition: Several spines preserved in the matrix of the adoral surface (Clark & Twitchell, 1915).
SPECIMENS STUDIED & CONDITION: Syntypes USNM 103708 and 103708A. Two specimens embedded in a single mass of indurated marl; one shows the adoral surface, the other the aboral surface.
ETYMOLOGY
From the Latin planulata (flat or level), referring to the distinctly flattened upper surface.
REMARKS & COMPARISONS
Remarks: Lambert (1914), in a review of Clark's monograph, noted that O. planulata seems difficult to distinguish from O. occidentalis (Cragin), suggesting a close relationship or potential synonymy. However, Adkins (1928) maintained it as a distinct species, noting it is "smaller, less elevated, and less pentagonal" than O. occidentalis.
Comparisons:
- Orthopsis occidentalis: O. planulata is more circular (less pentagonal) and significantly more depressed (flatter) than the pyramido-hemispherical O. occidentalis.
Remarks: (02-2026) A specimen was found in the xxxx formation in xxxxx County by Lance Southwick, of xxxxxx,
