Phymosoma hilli (Clark, 1891)
Plate: PhHi-10
Series: Upper Cretaceous Group: Austin Formation: Austin Chalk
Locale: Unknown County: Bell Stage: Santonian
Length: 31.9 mm Height: 13.1 mm
Specimen in photos: U.S.N.M. 8311 Holotype
Repository: Paleobiology Depart. NMNH, Smithsonian Institution
Plate: PhHi-20
Series: Upper Cretaceous Group: Austin Formation: Burditt
Locale: Austin County: Travis Stage: Santonian
Length: 33.8 mm Height: 16.9 mm
Collector: Ed Elliott
Repository: Private Collection
HOLOTYPE INFO:
Holotype: USNM 8311 (Clark, 1893).
Locality: Bell County (per Specimen Label PhHi-10); Austin, Travis County (per Clark, 1893).
Stratigraphy: Austin Chalk.
SYNONYMY
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Calycina Gregory, 1900
Order: Phymosomatoida Mortensen, 1904
Family: Phymosomatidae Pomel, 1883
Genus: PHYMOSOMA Haime, 1853
Species: Phymosoma hilli (Clark, 1893)
TYPE SPECIES: Diadema priscum Agassiz, 1840
DIAGNOSIS
Test subpentagonal and depressed; sides inflated (Clark, 1893). Ambulacra prominent with two rows of primary tubercles (Clark, 1915). Pore pairs are uniserial below and bigeminal (biserial) on the upper surface (Clark, 1893). Interambulacra possess two rows of primary tubercles equal in size to those of the ambulacra (Clark, 1893). Tubercles are imperforate (Ikins, 1940; Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Austin
Formations: Austin Chalk; Burditt Formation.
Stratigraphic Units: Upper Cretaceous, Santonian.
Counties: Bell, Travis. Hays
Abundance: Scarce.
DESCRIPTION
TOP: Length, width, height: 33.8 mm L × 16.9 mm H (PhHi-20). Top shape: Subpentagonal outline (Clark, 1893); circular to slightly subpentagonal. Top domed: Depressed on upper surface (Clark, 1893); top flat for about 40% of total width.
SIDE: Ambitus: Moderately inflated (Clark, 1893); positioned 40% of height from the bottom. Side shape: Slopes more abruptly below the ambitus than above.
BOTTOM: Bottom shape: Depressed/flattened on lower surface (Clark, 1893); flat for 70% of total width. Concavity: Somewhat concave toward the mouth opening (Clark, 1893).
AMB: Amb shape: Broad, very prominent (Clark, 1893); lanceolate. Amb arrangement: Two rows of large tubercles, 12 or 13 in each row (Clark, 1893); decrease rapidly from ambitus toward apical disk and peristome (Clark, 1915). Amb width: Widest at ambitus; narrows slightly at bottom, much more at top.
PORE PAIRS: Arrangement: Single pairs (uniserial) on the lower surface (Clark, 1893). Bigeminal (biserial) on the upper surface near the apical system (Clark, 1893). Erratic and crowded near peristome.
TUBERCLES: Primary Perforated: No (Imperforate) (Ikins, 1940; Cooke, 1953); described as deepy perforated in original text (Clark, 1893). Primary Crenulate: Distinctly crenulated (Clark, 1893). Distribution: Two rows in ambulacra; two rows in interambulacra. Scrobicular Tubercles: Small secondary tubercles cover intervening space (Clark, 1893). Areolas: Narrow, circular, and elevated (Clark, 1893).
GRANULES: Distribution: Sparsely scattered granules (Clark, 1893); granules along both medial and adradial ridges.
FASCIOLE: Absent.
INTERAMB: Width: Narrow and appear flattened compared to the projecting ambulacra (Clark, 1893). Arrangement: Two rows of primary tubercles of equal size to those of the ambulacra; 10 or 11 in each row (Clark, 1893).
APICAL SYSTEM: Size: Takes up about 35% of top. Shape: Broad and pentagonal (Clark, 1893). Plating: Angles occur at the point of the medial suture of the interambulacra (Clark, 1893).
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Broad (Clark, 1915); narrow (Clark, 1893); diameter about 35% of bottom. Shape: Circular (Clark, 1893). Lip: Divided by ten incisions into well-defined lobes; ambulacral lobes broader (Clark, 1893). Secondary indentations halfway between each notch.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION:
ETYMOLOGY
Named in honor of Robert T. Hill (1858–1941), the "Father of Texas Cretaceous Geology."
REMARKS & COMPARISONS
Remarks: This species was originally described as Diplopodia hilli by Clark (1893), who erroneously described the tubercles as perforate. Ikins (1940) recognized that Austin Chalk specimens were imperforate and proposed the name Phymosoma bybeei, assuming Clark's hilli was a different (perforate) species. Cooke (1953) re-examined Clark's holotype (USNM 8311) and confirmed the tubercles are indeed imperforate (Phymosomatid), proving that Clark had simply misdescribed the feature. Therefore, P. hilli is the valid senior synonym, and P. bybeei is a junior synonym.
Measurement Discrepancy: Clark (1915) lists the diameter as 20 mm. The actual Holotype USNM 8311 measures 31.9 mm (per PhHi-10 label), and the Ed Elliott specimen (PhHi-20) measures 33.8 mm.
Locality Conflict: Clark (1893) lists "Austin"; User data for USNM 8311 lists "Bell County." Both are listed in the header/Holotype info. Austin could have referred to Austin Chalk formation which is present in Bell County.. Cragin (1893) also wrote “common in the Austin limestone of Fairview Park, South Austin.
Comparisons:
Plate: PhHi-10
Series: Upper Cretaceous Group: Austin Formation: Austin Chalk
Locale: Unknown County: Bell Stage: Santonian
Length: 31.9 mm Height: 13.1 mm
Specimen in photos: U.S.N.M. 8311 Holotype
Repository: Paleobiology Depart. NMNH, Smithsonian Institution
Plate: PhHi-20
Series: Upper Cretaceous Group: Austin Formation: Burditt
Locale: Austin County: Travis Stage: Santonian
Length: 33.8 mm Height: 16.9 mm
Collector: Ed Elliott
Repository: Private Collection
HOLOTYPE INFO:
Holotype: USNM 8311 (Clark, 1893).
Locality: Bell County (per Specimen Label PhHi-10); Austin, Travis County (per Clark, 1893).
Stratigraphy: Austin Chalk.
SYNONYMY
- Diplopodia hilli Clark, 1893
- Cyphosoma hilli (Clark) Clark, 1915
- Phymosoma bybeei Ikins, 1940
- Phymosoma hilli (Clark) Cooke, 1953
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Calycina Gregory, 1900
Order: Phymosomatoida Mortensen, 1904
Family: Phymosomatidae Pomel, 1883
Genus: PHYMOSOMA Haime, 1853
Species: Phymosoma hilli (Clark, 1893)
TYPE SPECIES: Diadema priscum Agassiz, 1840
DIAGNOSIS
Test subpentagonal and depressed; sides inflated (Clark, 1893). Ambulacra prominent with two rows of primary tubercles (Clark, 1915). Pore pairs are uniserial below and bigeminal (biserial) on the upper surface (Clark, 1893). Interambulacra possess two rows of primary tubercles equal in size to those of the ambulacra (Clark, 1893). Tubercles are imperforate (Ikins, 1940; Cooke, 1953).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Austin
Formations: Austin Chalk; Burditt Formation.
Stratigraphic Units: Upper Cretaceous, Santonian.
Counties: Bell, Travis. Hays
Abundance: Scarce.
DESCRIPTION
TOP: Length, width, height: 33.8 mm L × 16.9 mm H (PhHi-20). Top shape: Subpentagonal outline (Clark, 1893); circular to slightly subpentagonal. Top domed: Depressed on upper surface (Clark, 1893); top flat for about 40% of total width.
SIDE: Ambitus: Moderately inflated (Clark, 1893); positioned 40% of height from the bottom. Side shape: Slopes more abruptly below the ambitus than above.
BOTTOM: Bottom shape: Depressed/flattened on lower surface (Clark, 1893); flat for 70% of total width. Concavity: Somewhat concave toward the mouth opening (Clark, 1893).
AMB: Amb shape: Broad, very prominent (Clark, 1893); lanceolate. Amb arrangement: Two rows of large tubercles, 12 or 13 in each row (Clark, 1893); decrease rapidly from ambitus toward apical disk and peristome (Clark, 1915). Amb width: Widest at ambitus; narrows slightly at bottom, much more at top.
PORE PAIRS: Arrangement: Single pairs (uniserial) on the lower surface (Clark, 1893). Bigeminal (biserial) on the upper surface near the apical system (Clark, 1893). Erratic and crowded near peristome.
TUBERCLES: Primary Perforated: No (Imperforate) (Ikins, 1940; Cooke, 1953); described as deepy perforated in original text (Clark, 1893). Primary Crenulate: Distinctly crenulated (Clark, 1893). Distribution: Two rows in ambulacra; two rows in interambulacra. Scrobicular Tubercles: Small secondary tubercles cover intervening space (Clark, 1893). Areolas: Narrow, circular, and elevated (Clark, 1893).
GRANULES: Distribution: Sparsely scattered granules (Clark, 1893); granules along both medial and adradial ridges.
FASCIOLE: Absent.
INTERAMB: Width: Narrow and appear flattened compared to the projecting ambulacra (Clark, 1893). Arrangement: Two rows of primary tubercles of equal size to those of the ambulacra; 10 or 11 in each row (Clark, 1893).
APICAL SYSTEM: Size: Takes up about 35% of top. Shape: Broad and pentagonal (Clark, 1893). Plating: Angles occur at the point of the medial suture of the interambulacra (Clark, 1893).
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Broad (Clark, 1915); narrow (Clark, 1893); diameter about 35% of bottom. Shape: Circular (Clark, 1893). Lip: Divided by ten incisions into well-defined lobes; ambulacral lobes broader (Clark, 1893). Secondary indentations halfway between each notch.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION:
- Holotype (PhHi-10): USNM 8311. Length 31.9 mm, Height 13.1 mm. Bell County (per label) / Austin (per Clark).
- Figured Specimen (PhHi-20): Collection of Ed Elliott. Length 33.8 mm, Height 16.9 mm. Austin, Travis County (Burditt Fm).
- Original Drawings (Clark): Length 3/4 inch (~19 mm); Height 5/16 inch (~8 mm). (Note: Drawings do not match current Holotype dimensions).
ETYMOLOGY
Named in honor of Robert T. Hill (1858–1941), the "Father of Texas Cretaceous Geology."
REMARKS & COMPARISONS
Remarks: This species was originally described as Diplopodia hilli by Clark (1893), who erroneously described the tubercles as perforate. Ikins (1940) recognized that Austin Chalk specimens were imperforate and proposed the name Phymosoma bybeei, assuming Clark's hilli was a different (perforate) species. Cooke (1953) re-examined Clark's holotype (USNM 8311) and confirmed the tubercles are indeed imperforate (Phymosomatid), proving that Clark had simply misdescribed the feature. Therefore, P. hilli is the valid senior synonym, and P. bybeei is a junior synonym.
Measurement Discrepancy: Clark (1915) lists the diameter as 20 mm. The actual Holotype USNM 8311 measures 31.9 mm (per PhHi-10 label), and the Ed Elliott specimen (PhHi-20) measures 33.8 mm.
Locality Conflict: Clark (1893) lists "Austin"; User data for USNM 8311 lists "Bell County." Both are listed in the header/Holotype info. Austin could have referred to Austin Chalk formation which is present in Bell County.. Cragin (1893) also wrote “common in the Austin limestone of Fairview Park, South Austin.
Comparisons:
- Phymosoma texanum: P. hilli is separated by its smaller size, subpentagonal form, and having two instead of four rows of primary tubercles (Clark, 1893).
