Hemiaster bexari (Clark, 1915)
Plate: HeBex-10
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maastrichtian
Length: 22.9 mm Width: 21.6 mm Height: 15.6 mm
Specimen in photo: U.S.N.M. 8330 Holotype
Repository: National Museum of Natural History (NMNH), Smithsonian Institution
Plate: HeBex-10
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maastrichtian
Length: 22.9 mm Width: 21.6 mm Height: 15.6 mm
Specimen in photo: USNM 8330 (Holotype)
HOLOTYPE INFO:
Holotype: USNM 8330 - National Museum of Natural History, Smithsonian Institution (Clark & Twitchell, 1915)
Locality: Bexar County, Texas (Clark & Twitchell, 1915)
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 bexari (Clark, 1915)
TYPE SPECIES: Spatangus bufo Brongniart, 1822
DIAGNOSIS
Test small, upper surface nearly flat, elevated, lower surface rounded; sides inflated. Apex nearly central. Posterolateral ambulacra very short; interambulacra prominent. Peristome small, only slightly depressed, near anterior margin. Periproct small, situated high on truncated surface of posterior margin (Clark & Twitchell, 1915).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Navarro ; Washita (Original Description, but corrected to Navarro by Cooke, 1953) (Clark & Twitchell, 1915)
Formations: Corsicana Formation
Stratigraphic Units: Upper Cretaceous, Maastrichtian
Counties: Bexar County (Clark & Twitchell, 1915)
DESCRIPTION
TOP: Length, width, height: 22.9 mm L × 21.6 mm W × 15.6 mm H (Clark & Twitchell, 1915)
Top shape: Broad, nearly flat upper surface (Clark & Twitchell, 1915)
Top domed: Rising toward the center, which is slightly elevated (Clark & Twitchell, 1915)
SIDE: Side shape: Sides inflated (Clark & Twitchell, 1915)
BOTTOM: Bottom shape: Lower surface rounded, sloping from near the center in all directions (Clark & Twitchell, 1915)
AMB: Amb shape: Anterior ambulacrum broad and shallow (Clark & Twitchell, 1915)
Amb arrangement: Ambulacra unequal; posterolateral pair very short (Clark & Twitchell, 1915)
Amb primary zones: Poriferous zones broad and shallow, but little depressed (Clark & Twitchell, 1915)
TUBERCLES: Primary tubercles: Surface covered with small tubercles (Clark & Twitchell, 1915)
FASCIOLE: Peripetalous fasciole distinct (Clark & Twitchell, 1915)
APICAL SYSTEM: Location: Nearly central (Clark & Twitchell, 1915)
PERIPROCT (ANUS): Shape & Size: Small (Clark & Twitchell, 1915)
Location: Situated high on the truncated surface of the posterior margin (Clark & Twitchell, 1915)
PERISTOME (MOUTH): Size: Small (Clark & Twitchell, 1915)
Location: Near the anterior margin (Clark & Twitchell, 1915)
Sunken: Only slightly depressed (Clark & Twitchell, 1915)
Sternal Plates: Not symmetrical, left sternal plate dominating in size and arrangement above right sternal plate.
SPECIMENS STUDIED & CONDITION Holotype USNM 8330.
ETYMOLOGY
Named for Bexar County, Texas, the type locality (Clark, 1915).
REMARKS & COMPARISONS
Remarks: This species can be separated from Hemiaster wetherbyi because there are no large beads between the pore pairs in the unpaired ambulacrum.
Cooke lumped the two species together, he said "the holotype of Hemiaster bexari, from Bexar County, Tex., has been crushed, but it retains enough features to show that it is the same species as the type of Hemiaster wetherbyi... The shape of the test, the petals, and the fascioles are the same in both."
Comparisons: Cooke (1953) typically included H. bexari in his study of Upper Cretaceous echinoids, implicitly correcting the original "Washita" assignment.
Remarks: (02-2026). Some authors have reassigned to the Genus Bolbaster. The sternal plates in the Bolaster are symmetrical, whereas in Hemiasters the sternal plates are not symmetrical with the left sternal plate dominating in size and arrangement above the right sternal plate.
Plate: HeBex-10
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maastrichtian
Length: 22.9 mm Width: 21.6 mm Height: 15.6 mm
Specimen in photo: U.S.N.M. 8330 Holotype
Repository: National Museum of Natural History (NMNH), Smithsonian Institution
Plate: HeBex-10
Series: Upper Cretaceous Group: Navarro Formation: Corsicana
Locale: San Antonio County: Bexar Stage: Maastrichtian
Length: 22.9 mm Width: 21.6 mm Height: 15.6 mm
Specimen in photo: USNM 8330 (Holotype)
HOLOTYPE INFO:
Holotype: USNM 8330 - National Museum of Natural History, Smithsonian Institution (Clark & Twitchell, 1915)
Locality: Bexar County, Texas (Clark & Twitchell, 1915)
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 bexari (Clark, 1915)
TYPE SPECIES: Spatangus bufo Brongniart, 1822
DIAGNOSIS
Test small, upper surface nearly flat, elevated, lower surface rounded; sides inflated. Apex nearly central. Posterolateral ambulacra very short; interambulacra prominent. Peristome small, only slightly depressed, near anterior margin. Periproct small, situated high on truncated surface of posterior margin (Clark & Twitchell, 1915).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Navarro ; Washita (Original Description, but corrected to Navarro by Cooke, 1953) (Clark & Twitchell, 1915)
Formations: Corsicana Formation
Stratigraphic Units: Upper Cretaceous, Maastrichtian
Counties: Bexar County (Clark & Twitchell, 1915)
DESCRIPTION
TOP: Length, width, height: 22.9 mm L × 21.6 mm W × 15.6 mm H (Clark & Twitchell, 1915)
Top shape: Broad, nearly flat upper surface (Clark & Twitchell, 1915)
Top domed: Rising toward the center, which is slightly elevated (Clark & Twitchell, 1915)
SIDE: Side shape: Sides inflated (Clark & Twitchell, 1915)
BOTTOM: Bottom shape: Lower surface rounded, sloping from near the center in all directions (Clark & Twitchell, 1915)
AMB: Amb shape: Anterior ambulacrum broad and shallow (Clark & Twitchell, 1915)
Amb arrangement: Ambulacra unequal; posterolateral pair very short (Clark & Twitchell, 1915)
Amb primary zones: Poriferous zones broad and shallow, but little depressed (Clark & Twitchell, 1915)
TUBERCLES: Primary tubercles: Surface covered with small tubercles (Clark & Twitchell, 1915)
FASCIOLE: Peripetalous fasciole distinct (Clark & Twitchell, 1915)
APICAL SYSTEM: Location: Nearly central (Clark & Twitchell, 1915)
PERIPROCT (ANUS): Shape & Size: Small (Clark & Twitchell, 1915)
Location: Situated high on the truncated surface of the posterior margin (Clark & Twitchell, 1915)
PERISTOME (MOUTH): Size: Small (Clark & Twitchell, 1915)
Location: Near the anterior margin (Clark & Twitchell, 1915)
Sunken: Only slightly depressed (Clark & Twitchell, 1915)
Sternal Plates: Not symmetrical, left sternal plate dominating in size and arrangement above right sternal plate.
SPECIMENS STUDIED & CONDITION Holotype USNM 8330.
ETYMOLOGY
Named for Bexar County, Texas, the type locality (Clark, 1915).
REMARKS & COMPARISONS
Remarks: This species can be separated from Hemiaster wetherbyi because there are no large beads between the pore pairs in the unpaired ambulacrum.
Cooke lumped the two species together, he said "the holotype of Hemiaster bexari, from Bexar County, Tex., has been crushed, but it retains enough features to show that it is the same species as the type of Hemiaster wetherbyi... The shape of the test, the petals, and the fascioles are the same in both."
Comparisons: Cooke (1953) typically included H. bexari in his study of Upper Cretaceous echinoids, implicitly correcting the original "Washita" assignment.
Remarks: (02-2026). Some authors have reassigned to the Genus Bolbaster. The sternal plates in the Bolaster are symmetrical, whereas in Hemiasters the sternal plates are not symmetrical with the left sternal plate dominating in size and arrangement above the right sternal plate.
