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Rhynchostreon
Classification
Phylum:
Mollusca
Class:
None
Subclass:
Pteriomorphia
Order:
Pterioida
Suborder:
Ostreina (oysters)
Superfamily:
Ostreacea
Family:
Gryphaeidae
Subfamily:
Exogyrinae - TRIBE Exogyrini
Formal Genus Name and Reference:
Rhynchostreon BAYLE, 1878, pl. 138 explanation
Type Species:
R. chaperi Bayle, 1878, pl. 138, fig. 1-5 (=Gryphaea suborbiculata Lamarck, 1801, p. 398, G. columba Lamarck, 1819, v. 6, pt. 1, p. 98, R. suborbiculatum (Lamarck), SD DOUVILLÉ, 1879)
Images
(Click to enlarge in a new window)
Fig. J97,1. • R. SlIborbictliattlm (LAMARCK, 1801), Turon., France (Mosne, Departement Indre-et-Loire); I a-d, whitened for photography, various views, X0.7; Ie, same specimen, not whitened, post. view of umbonal region showing beekite silicification centers, X 2; If, same specimen, whitened, same view, showing absence of attachment area and roughness caused by local silicification, X2 (Stenzel, n; specimen from Naturhistorisches Mus., Basel, Switz.).
Synonyms
Rhyncostreon
Geographic Distribution
N. Am. (Mexico-Texas-N.Mexico-Colo.-Minn.-Va. subsurface) -Eu. (Eng.-France-Ger.-Czech.-Pol.-Hung.-USSR-Spain-Port.-Sardinia-Switz. - Aus.) - Asia (India-Syria)
Age Range
Beginning Stage in Treatise Usage:
U.Cret.(Cenoman.),
Beginning International Stage:
Cenomanian
Fraction Up In Beginning Stage:
0
Beginning Date:
100.5
Ending Stage in Treatise Usage:
U.Cret.(Turon.),
Ending International Stage:
Turonian
Fraction Up In Ending Stage:
100
Ending Date:
89.39
Description
Medium-sized (up to 13 cm high), highly inequivalve, LV smooth and highly convex, especially so in anteroposterior cross section, LV beak narrow, so greatly elevated above hinge that valve height exceeds length (generally height is 108 percent of length, but may reach 143 percent), highly incoiled (up to 2 volutions), opisthogyral although it is more nearly orthogyral than LV beak of other genera in the Exogyrinae. Surface of LV very smooth, with faint and smooth growth wrinkles and closely and smoothly appressed growth squamae. Rounded keel present on LV only in its earliest growth stage, when about 1 em. high; keel more noticeable in individuals having many fine radial costules, which are also restricted to earliest growth stage. Broad and shallow radial sulcus starting on LV in mature growth stage, easily overlooked. Attachment area absent or very small, at best 9 by 13 mm. in size. RV suborbicular to horizontal elliptical, longer than high, flat in dorsoventral direction, concave in anteroposterior direction and devoid of costules, with flat spiral umbo and smooth with smoothly appressed growth squamae, no reflexed growth squamae at anterior valve margin. Mature to old individuals have broad gentle terebratuloid fold at ventral margin. Adductor muscle imprint orbicular. Ligamental area very narrow. No chomata. [Although many authors use the species name columba, the earliest available name is suborbiculatum.]
References
Museum or Author Information
Classification
Phylum:
Mollusca
Class:
None
Subclass:
Pteriomorphia
Order:
Pterioida
Suborder:
Ostreina (oysters)
Superfamily:
Ostreacea
Family:
Gryphaeidae
Subfamily:
Exogyrinae - TRIBE Exogyrini
Formal Genus Name and Reference:
Rhynchostreon BAYLE, 1878, pl. 138 explanation
Type Species:
R. chaperi Bayle, 1878, pl. 138, fig. 1-5 (=Gryphaea suborbiculata Lamarck, 1801, p. 398, G. columba Lamarck, 1819, v. 6, pt. 1, p. 98, R. suborbiculatum (Lamarck), SD DOUVILLÉ, 1879)
Images
(Click to enlarge in a new window)
Fig. J97,1. • R. SlIborbictliattlm (LAMARCK, 1801), Turon., France (Mosne, Departement Indre-et-Loire); I a-d, whitened for photography, various views, X0.7; Ie, same specimen, not whitened, post. view of umbonal region showing beekite silicification centers, X 2; If, same specimen, whitened, same view, showing absence of attachment area and roughness caused by local silicification, X2 (Stenzel, n; specimen from Naturhistorisches Mus., Basel, Switz.).
Synonyms
Rhyncostreon
Geographic Distribution
N. Am. (Mexico-Texas-N.Mexico-Colo.-Minn.-Va. subsurface) -Eu. (Eng.-France-Ger.-Czech.-Pol.-Hung.-USSR-Spain-Port.-Sardinia-Switz. - Aus.) - Asia (India-Syria)
Age Range
Beginning Stage in Treatise Usage:
U.Cret.(Cenoman.),
Beginning International Stage:
Cenomanian
Fraction Up In Beginning Stage:
0
Beginning Date:
100.5
Ending Stage in Treatise Usage:
U.Cret.(Turon.),
Ending International Stage:
Turonian
Fraction Up In Ending Stage:
100
Ending Date:
89.39
Description
Medium-sized (up to 13 cm high), highly inequivalve, LV smooth and highly convex, especially so in anteroposterior cross section, LV beak narrow, so greatly elevated above hinge that valve height exceeds length (generally height is 108 percent of length, but may reach 143 percent), highly incoiled (up to 2 volutions), opisthogyral although it is more nearly orthogyral than LV beak of other genera in the Exogyrinae. Surface of LV very smooth, with faint and smooth growth wrinkles and closely and smoothly appressed growth squamae. Rounded keel present on LV only in its earliest growth stage, when about 1 em. high; keel more noticeable in individuals having many fine radial costules, which are also restricted to earliest growth stage. Broad and shallow radial sulcus starting on LV in mature growth stage, easily overlooked. Attachment area absent or very small, at best 9 by 13 mm. in size. RV suborbicular to horizontal elliptical, longer than high, flat in dorsoventral direction, concave in anteroposterior direction and devoid of costules, with flat spiral umbo and smooth with smoothly appressed growth squamae, no reflexed growth squamae at anterior valve margin. Mature to old individuals have broad gentle terebratuloid fold at ventral margin. Adductor muscle imprint orbicular. Ligamental area very narrow. No chomata. [Although many authors use the species name columba, the earliest available name is suborbiculatum.]