Domechinus chelonium (Cooke, 1953)
Plate: DoCh-10
Series: Upper Cretaceous Group: Navarro Formation: Escondido
Locale: Indio Ranch County: Maverick Stage: Maastrichtian
Length: 30.4 mm Width: 28.0 mm Height: 15.1 mm
Specimen in photo: USNM 108377 (Holotype)
Repository: National Museum of Natural History (NMNH), Smithsonian Institution
HOLOTYPE INFO:
Holotype: USNM 108377 — National Museum of Natural History, Smithsonian Institution (Cooke, 1953)
Locality: Indio Ranch, Maverick County, Texas (Cooke, 1953)
SYNONYMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Neognathostomata Smith, 1981
Order: Cassiduloida Claus, 1880
Family: Faujasiidae Lambert, 1905
Genus: DOMECHINUS Kier, 1962
Species: Domechinus chelonium (Cooke, 1953)
TYPE SPECIES: Domechinus phililppi (Forbes, 1844)
DIAGNOSIS
Test medium-sized with a tumid upper surface and slightly concave lower surface; expanded margin turned down. Horizontal outline semicircular in front, sides straight, V-shaped behind. Petals lanceolate, nearly equal. Periproct terminal, indenting the margin (Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Navarro
Formations: Escondido Formation
Stratigraphic Units: Upper Cretaceous, Maastrichtian
Counties: Maverick County
DESCRIPTION
TOP: Length, width, height: 30.4 mm L × 28.0 mm W × 15.1 mm H (Cooke, 1953)
Top shape: Horizontal outline semicircular in front, sides straight, V-shaped behind (Cooke, 1953)
Top domed: Upper surface tumid (Cooke, 1953)
SIDE: Ambitus: Margin sharp; expanded and turned down (Cooke, 1953)
BOTTOM: Bottom shape: Slightly concave (Cooke, 1953)
AMB: Amb shape: Petals lanceolate, nearly equal in length; extending little more than halfway to the margin (Cooke, 1953)
Amb width: Poriferous zones nearly closed at the outer ends, somewhat wider open at the inner ends (Cooke, 1953)
PORE PAIRS: Shape: Inner row circular; outer row slightly elongate (Cooke, 1953)
Conjugate vs Nonconjugate: Pores conjugate; zygopores oblique with respect to the median suture of the petal (Cooke, 1953)
APICAL SYSTEM: Location: Central (Cooke, 1953)
Plates: Monobasal (plates fused) (Cooke, 1953)
Genital pores: Four genital pores (Cooke, 1953)
PERIPROCT (ANUS): Shape & Size: Transversely elongated; small (Cooke, 1953)
Location: Terminal; indenting the margin as viewed from above but turned slightly downward (Cooke, 1953)
PERISTOME (MOUTH): Location: Central (Cooke, 1953)
Lip: Bourrelets long and pointed like those of Hardouinia (Cooke, 1953)
Phyllodes: Longer than wide (Cooke, 1953)
SPECIMENS STUDIED & CONDITION
Specimen condition: Holotype USNM 108377 .
ETYMOLOGY: The specific name is a Latin noun meaning, literally, a tortoise shell (Cooke, 1953).
REMARKS & COMPARISONS
Remarks: Originally described by Cooke (1953) as Faujasia chelonium. It was later transferred to the genus Domechinus by Kier (1962) based on the shape of the test and petal arrangement.
Comparisons:
Plate: DoCh-10
Series: Upper Cretaceous Group: Navarro Formation: Escondido
Locale: Indio Ranch County: Maverick Stage: Maastrichtian
Length: 30.4 mm Width: 28.0 mm Height: 15.1 mm
Specimen in photo: USNM 108377 (Holotype)
Repository: National Museum of Natural History (NMNH), Smithsonian Institution
HOLOTYPE INFO:
Holotype: USNM 108377 — National Museum of Natural History, Smithsonian Institution (Cooke, 1953)
Locality: Indio Ranch, Maverick County, Texas (Cooke, 1953)
SYNONYMY
- Faujasia chelonium Cooke, 1953
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Neognathostomata Smith, 1981
Order: Cassiduloida Claus, 1880
Family: Faujasiidae Lambert, 1905
Genus: DOMECHINUS Kier, 1962
Species: Domechinus chelonium (Cooke, 1953)
TYPE SPECIES: Domechinus phililppi (Forbes, 1844)
DIAGNOSIS
Test medium-sized with a tumid upper surface and slightly concave lower surface; expanded margin turned down. Horizontal outline semicircular in front, sides straight, V-shaped behind. Petals lanceolate, nearly equal. Periproct terminal, indenting the margin (Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Navarro
Formations: Escondido Formation
Stratigraphic Units: Upper Cretaceous, Maastrichtian
Counties: Maverick County
DESCRIPTION
TOP: Length, width, height: 30.4 mm L × 28.0 mm W × 15.1 mm H (Cooke, 1953)
Top shape: Horizontal outline semicircular in front, sides straight, V-shaped behind (Cooke, 1953)
Top domed: Upper surface tumid (Cooke, 1953)
SIDE: Ambitus: Margin sharp; expanded and turned down (Cooke, 1953)
BOTTOM: Bottom shape: Slightly concave (Cooke, 1953)
AMB: Amb shape: Petals lanceolate, nearly equal in length; extending little more than halfway to the margin (Cooke, 1953)
Amb width: Poriferous zones nearly closed at the outer ends, somewhat wider open at the inner ends (Cooke, 1953)
PORE PAIRS: Shape: Inner row circular; outer row slightly elongate (Cooke, 1953)
Conjugate vs Nonconjugate: Pores conjugate; zygopores oblique with respect to the median suture of the petal (Cooke, 1953)
APICAL SYSTEM: Location: Central (Cooke, 1953)
Plates: Monobasal (plates fused) (Cooke, 1953)
Genital pores: Four genital pores (Cooke, 1953)
PERIPROCT (ANUS): Shape & Size: Transversely elongated; small (Cooke, 1953)
Location: Terminal; indenting the margin as viewed from above but turned slightly downward (Cooke, 1953)
PERISTOME (MOUTH): Location: Central (Cooke, 1953)
Lip: Bourrelets long and pointed like those of Hardouinia (Cooke, 1953)
Phyllodes: Longer than wide (Cooke, 1953)
SPECIMENS STUDIED & CONDITION
Specimen condition: Holotype USNM 108377 .
ETYMOLOGY: The specific name is a Latin noun meaning, literally, a tortoise shell (Cooke, 1953).
REMARKS & COMPARISONS
Remarks: Originally described by Cooke (1953) as Faujasia chelonium. It was later transferred to the genus Domechinus by Kier (1962) based on the shape of the test and petal arrangement.
Comparisons:
- Pygurostoma geometricum: D. chelonium is about half the size. Its outer pores are less elongated, posterolateral sides are straighter, margin is more expanded, periproct is more nearly terminal, and bourrelets are flatter (Cooke, 1953).
- Faujasia apicalis: D. chelonium has longer and broader petals, a more expanded margin, a more terminal periproct, and more pointed bourrelets (Cooke, 1953).
