Leiocidaris hemigranosa (Shumard, 1860)
Plate: PhHe-10
Series: Upper Cretaceous Group: Washita Formation: Boracho
Locale: Kent County: Culberson Stage: Cenomanian
Length: 43.6 mm Height: 33.9 mm
Specimen in photos: Collection of Ron Root
Repository: Private Collection
HOLOTYPE INFO:
Holotype: Originally described as Cidaris hemigranosus by Shumard (1860). Type material presumed lost.
Locality: Denton Creek, near the boundary of Grayson and Cooke Counties, Texas (Shumard, 1860).
Stratigraphy: Denton Formation / Washita Group.
SYNONYMY
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Cidaroidea Smith, 1984
Order: Cidaroida Claus, 1880
Family: Cidaridae Gray, 1825
Genus: LEIOCIDARIS Desor, 1855
Species: Leiocidaris hemigranosa (Shumard, 1860)
TYPE SPECIES: Cidaris imperialis Lamarck, 1816
DIAGNOSIS
Test very large (up to 100 mm) and subspherical. Ambulacra are narrow and sinuous with conjugate pore pairs united by a distinct furrow. Interambulacral tubercles are large, perforate, and non-crenulate (smooth). Extrascrobicular areas are wide and covered with large, scattered, flattened granules (Clark & Twitchell, 1915).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Boracho Formation; Denton Formation; Weno Formation; Main Street Limestone.
Stratigraphic Units: Lower Cretaceous (Albian) to Upper Cretaceous (Cenomanian).
Counties: Culberson, Grayson, Cooke, Denton.
Abundance: Uncommon; typically represented by large fragments or spines.
DESCRIPTION
TOP: Length, width, height: 43.6 mm L × 43.6 mm W × 33.9 mm H (Figured Specimen). Top shape: Circular. Top domed: Subspherical; considerably broader and more flattened on the oral than adoral side.
SIDE: Side shape: Inflated/Subspherical.
BOTTOM: Bottom shape: Flattened.
AMB: Amb shape: Narrow and sinuous. Amb arrangement: Six rows of granules between the poriferous avenues. Regular arrangement is not persistent; number increases near the middle and reduces toward the poles (Clark & Twitchell, 1915).
PORE PAIRS: Arrangement: Poriferous avenues are wide and deeply depressed. Shape: Conjugate; pores of each pair are united by a clearly defined, shallow furrow.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: No (Bosses smooth). Interambulacral Tubercles: Large and prominent, occupying the center of massive plates. Areolas: Deeply depressed, subcircular or slightly polygonal; occupy more than half the plate diameter. Surface is smooth. Bosses: Provided marginally with a sharp smooth ridge. Mamelons: Large, subspherical, with a deep perforation.
GRANULES: Distribution: Miliary space is wide and covered with large, irregularly shaped, flattened granules (some round, some oval). Interspersed with much smaller granules which increase in number along the plate margins.
FASCIOLE: Absent in Cidaroida.
INTERAMB: Width: Wide with massive plates.
APICAL SYSTEM: Condition: Often wanting (missing) in collected specimens.
PERIPROCT (ANUS): Unknown.
PERISTOME (MOUTH): Unknown in type material.
SPINES: Often found associated; large, heavy, and cylindrical.
SPECIMENS STUDIED & CONDITION: One specimen studied from the Collection of Ron Root. Note: The studied specimen (43.6 mm) is smaller than the maximum size reported for this species.
ETYMOLOGY
From the Latin hemi (half) + granosus (granular), likely referring to the extensive granulation on the extrascrobicular surfaces.
REMARKS & COMPARISONS
Remarks: This species is assigned to Leiocidaris Desor, 1855, following the classification of Clark & Twitchell (1915) and aligning with modern revisions by Vadet & Nicolleau and Smith & Kroh. While Cooke (1953) placed this species in Phyllacanthus, current taxonomy restricts Phyllacanthus primarily to Cenozoic and Recent forms. Cretaceous Cidarids possessing conjugate pores (connected by a furrow) and perforate, non-crenulate tubercles are more appropriately placed in Leiocidaris (or potentially Prionocidaris if spine morphology dictates). The distinct conjugate nature of the pores separates this from Cidaris sensu stricto.
Comparisons:
Plate: PhHe-10
Series: Upper Cretaceous Group: Washita Formation: Boracho
Locale: Kent County: Culberson Stage: Cenomanian
Length: 43.6 mm Height: 33.9 mm
Specimen in photos: Collection of Ron Root
Repository: Private Collection
HOLOTYPE INFO:
Holotype: Originally described as Cidaris hemigranosus by Shumard (1860). Type material presumed lost.
Locality: Denton Creek, near the boundary of Grayson and Cooke Counties, Texas (Shumard, 1860).
Stratigraphy: Denton Formation / Washita Group.
SYNONYMY
- Cidaris hemigranosus Shumard, 1860
- Leiocidaris hemigranosus (Shumard) Clark & Twitchell, 1915
- Phyllacanthus hemigranosus (Shumard) Cooke, 1953
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Cidaroidea Smith, 1984
Order: Cidaroida Claus, 1880
Family: Cidaridae Gray, 1825
Genus: LEIOCIDARIS Desor, 1855
Species: Leiocidaris hemigranosa (Shumard, 1860)
TYPE SPECIES: Cidaris imperialis Lamarck, 1816
DIAGNOSIS
Test very large (up to 100 mm) and subspherical. Ambulacra are narrow and sinuous with conjugate pore pairs united by a distinct furrow. Interambulacral tubercles are large, perforate, and non-crenulate (smooth). Extrascrobicular areas are wide and covered with large, scattered, flattened granules (Clark & Twitchell, 1915).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Boracho Formation; Denton Formation; Weno Formation; Main Street Limestone.
Stratigraphic Units: Lower Cretaceous (Albian) to Upper Cretaceous (Cenomanian).
Counties: Culberson, Grayson, Cooke, Denton.
Abundance: Uncommon; typically represented by large fragments or spines.
DESCRIPTION
TOP: Length, width, height: 43.6 mm L × 43.6 mm W × 33.9 mm H (Figured Specimen). Top shape: Circular. Top domed: Subspherical; considerably broader and more flattened on the oral than adoral side.
SIDE: Side shape: Inflated/Subspherical.
BOTTOM: Bottom shape: Flattened.
AMB: Amb shape: Narrow and sinuous. Amb arrangement: Six rows of granules between the poriferous avenues. Regular arrangement is not persistent; number increases near the middle and reduces toward the poles (Clark & Twitchell, 1915).
PORE PAIRS: Arrangement: Poriferous avenues are wide and deeply depressed. Shape: Conjugate; pores of each pair are united by a clearly defined, shallow furrow.
TUBERCLES: Primary Perforated: Yes. Primary Crenulate: No (Bosses smooth). Interambulacral Tubercles: Large and prominent, occupying the center of massive plates. Areolas: Deeply depressed, subcircular or slightly polygonal; occupy more than half the plate diameter. Surface is smooth. Bosses: Provided marginally with a sharp smooth ridge. Mamelons: Large, subspherical, with a deep perforation.
GRANULES: Distribution: Miliary space is wide and covered with large, irregularly shaped, flattened granules (some round, some oval). Interspersed with much smaller granules which increase in number along the plate margins.
FASCIOLE: Absent in Cidaroida.
INTERAMB: Width: Wide with massive plates.
APICAL SYSTEM: Condition: Often wanting (missing) in collected specimens.
PERIPROCT (ANUS): Unknown.
PERISTOME (MOUTH): Unknown in type material.
SPINES: Often found associated; large, heavy, and cylindrical.
SPECIMENS STUDIED & CONDITION: One specimen studied from the Collection of Ron Root. Note: The studied specimen (43.6 mm) is smaller than the maximum size reported for this species.
ETYMOLOGY
From the Latin hemi (half) + granosus (granular), likely referring to the extensive granulation on the extrascrobicular surfaces.
REMARKS & COMPARISONS
Remarks: This species is assigned to Leiocidaris Desor, 1855, following the classification of Clark & Twitchell (1915) and aligning with modern revisions by Vadet & Nicolleau and Smith & Kroh. While Cooke (1953) placed this species in Phyllacanthus, current taxonomy restricts Phyllacanthus primarily to Cenozoic and Recent forms. Cretaceous Cidarids possessing conjugate pores (connected by a furrow) and perforate, non-crenulate tubercles are more appropriately placed in Leiocidaris (or potentially Prionocidaris if spine morphology dictates). The distinct conjugate nature of the pores separates this from Cidaris sensu stricto.
Comparisons:
- Temnocidaris (Stereocidaris) hudspethensis: L. hemigranosa is clearly different due to the ambulacral plating; T. hudspethensis features one large, elongated wart and one outer granule on each ambulacral plate, whereas L. hemigranosa has six rows of granules.
