Plagiochasma texanum Smith and Rader, 2009
Plate: PlTe-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Bulverde County: Comal Stage: Albian
Length: 24.2 mm Width: 21.3 mm Height: 10.3 mm
Specimen in photo: NPL 83032 Hypotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Type: Refer to Smith & Rader (2009) for taxonomic description reference.
Figured Specimen: NPL 83032.
Locality: Bulverde, Comal County, Texas.
Stratigraphy: Glen Rose Formation.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Neognathostomata Smith, 1981
Order: Cassiduloida Claus, 1880
Family: Nucleolitidae L. Agassiz & Desor, 1847
Genus: PLAGIOCHASMA Pomel, 1883
Species: Plagiochasma texanum Smith & Rader, 2009
TYPE SPECIES: Nucleolites olfersii Agassiz, 1836
DIAGNOSIS
Test small, ovoid, and broader posteriorly. Characterized by a supramarginal periproct situated in a deep sulcus extending about 30% of the test length and cutting to the margin. Apical system is tetrabasal (Smith & Rader, 2009). Peristome is obliquely oval and depressed.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal.
Abundance: Uncommon.
DESCRIPTION
TOP: Length, width, height: 24.2 mm L × 21.3 mm W × 10.3 mm H. Top shape: Ovoid; broader posteriorly. Top domed: Apex positioned about 37% from the posterior end. Entire periproct seen from above.
SIDE: Ambitus: Positioned at about 45% of height from the adoral surface. Side shape: Sides curve to a rounded point.
BOTTOM: Bottom shape: Adoral side mostly flat along the margin.
AMB: Amb shape: All ambulacra are on the surface (flush) and petaloid; ends of petals are open. Amb arrangement: Ambulacra are narrowest at the apical system, widen quickly, narrow slightly, then widen again approaching the margin. All but the posterior paired ambulacra reach the margin.
PORE PAIRS: Shape: All sets of pore pairs include one round pore and one elongated pore until they reach the margin, where both become round (Smith & Rader, 2009).
TUBERCLES: Distribution: Very fine; largest toward the anterior end and ambitus.
GRANULES: (Not specified).
FASCIOLE: Absent.
APICAL SYSTEM: Type: Tetrabasal (Smith & Rader, 2009). Genital pores: Four gonopores. Plating: Madreporite is very large.
PERIPROCT (ANUS): Shape: Transversely oval. Location: Supramarginal; situated in a deep groove that is about 30% the length of the test. The groove cuts to the margin.
PERISTOME (MOUTH): Shape: Obliquely oval. Location: Slightly anterior of center. Sunken: Sits in a large depression. Size: Small.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype NPL 83032. Collected by William R. Thompson, Jr.
ETYMOLOGY
Named for the state of Texas.
REMARKS & COMPARISONS
Remarks: Smith & Rader (2009) validated the presence of this species in the Glen Rose Formation, providing specific analysis of the pore structures (round/elongate transition) and confirming the tetrabasal nature of the apical system.
Plate: PlTe-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Bulverde County: Comal Stage: Albian
Length: 24.2 mm Width: 21.3 mm Height: 10.3 mm
Specimen in photo: NPL 83032 Hypotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Type: Refer to Smith & Rader (2009) for taxonomic description reference.
Figured Specimen: NPL 83032.
Locality: Bulverde, Comal County, Texas.
Stratigraphy: Glen Rose Formation.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Neognathostomata Smith, 1981
Order: Cassiduloida Claus, 1880
Family: Nucleolitidae L. Agassiz & Desor, 1847
Genus: PLAGIOCHASMA Pomel, 1883
Species: Plagiochasma texanum Smith & Rader, 2009
TYPE SPECIES: Nucleolites olfersii Agassiz, 1836
DIAGNOSIS
Test small, ovoid, and broader posteriorly. Characterized by a supramarginal periproct situated in a deep sulcus extending about 30% of the test length and cutting to the margin. Apical system is tetrabasal (Smith & Rader, 2009). Peristome is obliquely oval and depressed.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Comal.
Abundance: Uncommon.
DESCRIPTION
TOP: Length, width, height: 24.2 mm L × 21.3 mm W × 10.3 mm H. Top shape: Ovoid; broader posteriorly. Top domed: Apex positioned about 37% from the posterior end. Entire periproct seen from above.
SIDE: Ambitus: Positioned at about 45% of height from the adoral surface. Side shape: Sides curve to a rounded point.
BOTTOM: Bottom shape: Adoral side mostly flat along the margin.
AMB: Amb shape: All ambulacra are on the surface (flush) and petaloid; ends of petals are open. Amb arrangement: Ambulacra are narrowest at the apical system, widen quickly, narrow slightly, then widen again approaching the margin. All but the posterior paired ambulacra reach the margin.
PORE PAIRS: Shape: All sets of pore pairs include one round pore and one elongated pore until they reach the margin, where both become round (Smith & Rader, 2009).
TUBERCLES: Distribution: Very fine; largest toward the anterior end and ambitus.
GRANULES: (Not specified).
FASCIOLE: Absent.
APICAL SYSTEM: Type: Tetrabasal (Smith & Rader, 2009). Genital pores: Four gonopores. Plating: Madreporite is very large.
PERIPROCT (ANUS): Shape: Transversely oval. Location: Supramarginal; situated in a deep groove that is about 30% the length of the test. The groove cuts to the margin.
PERISTOME (MOUTH): Shape: Obliquely oval. Location: Slightly anterior of center. Sunken: Sits in a large depression. Size: Small.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype NPL 83032. Collected by William R. Thompson, Jr.
ETYMOLOGY
Named for the state of Texas.
REMARKS & COMPARISONS
Remarks: Smith & Rader (2009) validated the presence of this species in the Glen Rose Formation, providing specific analysis of the pore structures (round/elongate transition) and confirming the tetrabasal nature of the apical system.
