Helcionopsis striata
Encyclopedia
Helcionopsis striata is an extinct species of paleozoic monoplacophora
n in the family Tryblidiidae
.
is rather strongly convex, acuminate-ovate in outline, broadly and regularly rounded behind, pointed in front where the apex
projects slightly beyond the margin of the aperture. The apex is incurved. The surface is marked by distinct, rounded, radiating lines, which in the outer half maintain an approximately equal size through bifurcation. There are about ten lines in 5 mm. The whole surface is with very fine concentric lines. Irregular wrinkles are marking stages of growth at intervals of 1 to 3 mm.
The length of the shell is 24.5 mm, width 19 mm and the height of the shell is 4.5 mm.
This species is closely related to the Upper Silurian Helcionopsis radiatum
, which is a little more convex, the anterior outline blunter and the apex more incurved.
. Also, though of smaller size in the Loraine group at Cincinnati, Ohio
.
Monoplacophora
Monoplacophora, meaning "bearing one plate", is a polyphyletic class of mollusks with a cap-like shell, living on the bottom of deep sea. Extant representatives were unknown until 1952; previously they were known only from the fossil record.- Definition :...
n in the family Tryblidiidae
Tryblidiidae
Pilina is an extinct family of paleozoic monoplacophorans in the superfamily Tryblidioidea.- Genera :Genera in the family Tryblidiidae include:* Tryblidium Lindström, 1880...
.
Shell description
The shellMollusc shell
The mollusc shell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes...
is rather strongly convex, acuminate-ovate in outline, broadly and regularly rounded behind, pointed in front where the apex
Apex (mollusc)
Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...
projects slightly beyond the margin of the aperture. The apex is incurved. The surface is marked by distinct, rounded, radiating lines, which in the outer half maintain an approximately equal size through bifurcation. There are about ten lines in 5 mm. The whole surface is with very fine concentric lines. Irregular wrinkles are marking stages of growth at intervals of 1 to 3 mm.
The length of the shell is 24.5 mm, width 19 mm and the height of the shell is 4.5 mm.
This species is closely related to the Upper Silurian Helcionopsis radiatum
Helcionopsis radiatum
Helcionopsis radiatum is an extinct species of paleozoic monoplacophoran in the family Tryblidiidae.This species was first named as Tryblidium radiatum and described from Silurian in crystalline limestone of Wialmsudd near Fårösund in Sweden by Gustaf Lindström in 1884. Lindsröm found only one...
, which is a little more convex, the anterior outline blunter and the apex more incurved.
Distribution
It is rare in the upper beds of the Cincinnati formation, Marion County, KentuckyMarion County, Kentucky
As of the census of 2000, there were 18,212 people, 6,613 households, and 4,754 families residing in the county. The population density was . There were 7,277 housing units at an average density of...
. Also, though of smaller size in the Loraine group at Cincinnati, Ohio
Ohio
Ohio is a Midwestern state in the United States. The 34th largest state by area in the U.S.,it is the 7th‑most populous with over 11.5 million residents, containing several major American cities and seven metropolitan areas with populations of 500,000 or more.The state's capital is Columbus...
.