Composita subtilita (Hall, 1852)

Composita subtilita (Hall, 1852)

General abundance:  Common

Discussion:

Species of the genus Composita have smooth shells, often with
periodic growth lines, and a weak or strong distinctive fold on
the margin of mature shells. Depending on the species, the fold
may be slight or very pronounced. This feature is known as a
fold and sulcus.

Viewer Comments #1

It appears to be similar to Composita trilobata Dunbar & Condra,
1932, based on similarity of specimens they illustrated and the one
you pictured. C. trilobata is one of the early Missourian species
named from a section near Winerset, Iowa. They called the unit
Cherryvale then, but the types are probably from what we now call
the Galesburg. You could probably call it

Composita sp. cf. C. trilobata Dunbar & Condra, 1932

I think that most of these Composita species grade into one another.

Dr. Roger K. Pabian

Viewer Comments: #2

Although this species is close to C. trilobata, it appears to be a
specimen of C. subtilita. Both species have a well developed fold
and sulcus, but C. trilobata has strong constrictions on the sides of
the fold that produce an appearance of 3 lobes on the margin of adult
shells, a feature that is lacking on this specimen. This specimen shows
a nice continuous curved margin with the beginning of a strong fold
and sulcus and it shows all of the features that characterize C. subtilita.
C. trilobata is known from older strata than your latest Desmoinesian
deposits, while C. subtilita is a very common brachiopod of the middle
to late Pennsylvanian, including the interval containing the Lake Neosho shale.

The study by Grinnell & Andrews (1964) compares and illustrates all
midcontinent Pennsylvanian and early Permian species of Composita.

Dr. Tom Yancey

References:

Dunbar, C. O. and Condra, G. E., 1932, ; Brachiopoda of the Pennsylvanian
System in Nebraska; Nebraska Geological Survey, Bull.5, p.363, pl.43, figs.7-13

Grinnell, R. S. and Andrews, G. W., 1964, Morphologic studies of the
brachiopod genus Composita; Journal of Paleontology, v. 38., p.235, pl.37-39

Hoare, R. D., 1961, Desmoinesian Brachiopoda and Mollusca from Southwest
Missouri; University of Missouri Press, p.89, pl.11, fig.20-25

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