Hemiaster cranium Cooke, 1946
Plate: HeCr-10
Series: Upper Cretaceous Group: Washita Formation: Weno
Locale: County: Johnson Stage: Albian
Length: 26.1 mm Width: 25.2 mm Height: 18.6 mm
Collector: William R. Thompson, Jr.
Repository: Private Collection
HOLOTYPE INFO:
Holotype: USNM 103912 — National Museum of Natural History, Smithsonian Institution (Cooke, 1946)
Locality: 3 miles east of Fort Worth, Tarrant County, Texas (Cooke, 1946)
Stratigraphy: Weno Limestone (Cooke, 1946)
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Spatangoida L. Agassiz, 1840
Family: Hemiasteridae L. Clark, 1917
Genus: HEMIASTER L. Agassiz, 1847
Species: Hemiaster cranium Cooke, 1946
TYPE SPECIES: Spatangus bufo Brongniart, 1822
DIAGNOSIS
Test high, cordate, inflated; posterior truncation vertical. Petals deep, straight; peripetalous fasciole distinct. Peristome far forward (Cooke, 1946).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Weno Limestone
Stratigraphic Units: Lower Cretaceous, Albian
Counties: Johnson, Tarrant (Cooke, 1946)
DESCRIPTION
TOP: Length, width, height: 26.1 mm L × 25.2 mm W × 18.6 mm H
Top shape: Ovate; cordate (Cooke, 1946). Widest point posterior of center.
Top domed: Very inflated; highest point posterior of center.
SIDE: Ambitus: Near midpoint.
Side shape: Tall; sides evenly rounded. Posterior truncated vertically.
Slope: Slopes on anterior end.
BOTTOM: Bottom flat: Flat.
AMB: Amb shape: Petals deep (very sunken), straight.
Amb arrangement: Paired ambs very short; anterior paired ambs slightly longer than posterior pair.
Amb primary zones: In anterior ambs, elongated pores point on inside of petals toward center of test; these two petals do not close on ends.
PORE PAIRS: Shape: Unpaired amb pores slightly elongated. Paired amb pores very elongated.
TUBERCLES: Primary tubercles: Largest on adoral surface, on either side of unpaired amb, and on plastron. Largest anteriorly on aboral side.
Primary Perforated: No (Generic Definition)
Primary Crenulate: Yes
Primary Areola shape: Sunken
Granules: Fine granulation covers entire test.
FASCIOLE: Weak peripetalous fasciole; passes straight across the interambulacra (Cooke, 1946).
APICAL SYSTEM: Size / Location: Small madreporite.
Genital pores: Four gonopores.
PERIPROCT (ANUS): Shape & Size: Small, vertically oval.
Location: High on truncated end.
Visibility: Seen from top.
PERISTOME (MOUTH): Shape: Transversely oval.
Location: Far forward (Cooke, 1946); half way between midpoint and anterior end.
Lip: Large raised lip pointing from center.
Sternal Plates: Not symmetrical, left sternal plate dominating in size and arrangement above right sternal plate.
SPECIMENS STUDIED & CONDITION
Specimen condition: Specimen collected by William R. Thompson, Jr.
ETYMOLOGY
From the Latin cranium, meaning "skull," referring to the high, domed shape of the test (Cooke, 1946).
REMARKS & COMPARISONS
Comparisons:
Plate: HeCr-10
Series: Upper Cretaceous Group: Washita Formation: Weno
Locale: County: Johnson Stage: Albian
Length: 26.1 mm Width: 25.2 mm Height: 18.6 mm
Collector: William R. Thompson, Jr.
Repository: Private Collection
HOLOTYPE INFO:
Holotype: USNM 103912 — National Museum of Natural History, Smithsonian Institution (Cooke, 1946)
Locality: 3 miles east of Fort Worth, Tarrant County, Texas (Cooke, 1946)
Stratigraphy: Weno Limestone (Cooke, 1946)
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Spatangoida L. Agassiz, 1840
Family: Hemiasteridae L. Clark, 1917
Genus: HEMIASTER L. Agassiz, 1847
Species: Hemiaster cranium Cooke, 1946
TYPE SPECIES: Spatangus bufo Brongniart, 1822
DIAGNOSIS
Test high, cordate, inflated; posterior truncation vertical. Petals deep, straight; peripetalous fasciole distinct. Peristome far forward (Cooke, 1946).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Weno Limestone
Stratigraphic Units: Lower Cretaceous, Albian
Counties: Johnson, Tarrant (Cooke, 1946)
DESCRIPTION
TOP: Length, width, height: 26.1 mm L × 25.2 mm W × 18.6 mm H
Top shape: Ovate; cordate (Cooke, 1946). Widest point posterior of center.
Top domed: Very inflated; highest point posterior of center.
SIDE: Ambitus: Near midpoint.
Side shape: Tall; sides evenly rounded. Posterior truncated vertically.
Slope: Slopes on anterior end.
BOTTOM: Bottom flat: Flat.
AMB: Amb shape: Petals deep (very sunken), straight.
Amb arrangement: Paired ambs very short; anterior paired ambs slightly longer than posterior pair.
Amb primary zones: In anterior ambs, elongated pores point on inside of petals toward center of test; these two petals do not close on ends.
PORE PAIRS: Shape: Unpaired amb pores slightly elongated. Paired amb pores very elongated.
TUBERCLES: Primary tubercles: Largest on adoral surface, on either side of unpaired amb, and on plastron. Largest anteriorly on aboral side.
Primary Perforated: No (Generic Definition)
Primary Crenulate: Yes
Primary Areola shape: Sunken
Granules: Fine granulation covers entire test.
FASCIOLE: Weak peripetalous fasciole; passes straight across the interambulacra (Cooke, 1946).
APICAL SYSTEM: Size / Location: Small madreporite.
Genital pores: Four gonopores.
PERIPROCT (ANUS): Shape & Size: Small, vertically oval.
Location: High on truncated end.
Visibility: Seen from top.
PERISTOME (MOUTH): Shape: Transversely oval.
Location: Far forward (Cooke, 1946); half way between midpoint and anterior end.
Lip: Large raised lip pointing from center.
Sternal Plates: Not symmetrical, left sternal plate dominating in size and arrangement above right sternal plate.
SPECIMENS STUDIED & CONDITION
Specimen condition: Specimen collected by William R. Thompson, Jr.
ETYMOLOGY
From the Latin cranium, meaning "skull," referring to the high, domed shape of the test (Cooke, 1946).
REMARKS & COMPARISONS
Comparisons:
- Hemiaster whitei (Clark): H. cranium is higher and shorter than H. whitei, and its posterior truncation is vertical rather than sloping (Cooke, 1946).
- Hemiaster elegans (Shumard): H. cranium is much smaller and relatively higher (Cooke, 1946).
