Cactocrinus glans
crinoid

Mississippian
Osagean Series
Upper Burlington Formation
Monroe County, Missouri

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Cactocrinus glans
originally placed in Actinocrinus
Actinocrinus glans (Hall, 1859) = Cactocrinus glans

I was puzzled by images illustrating Cactocrinus with a different appearance.

Viewer Comments:

This crinoid is Cactocrinus glans. Hall originally described it as Actinocrinus glans in 1860.
Wachsmuth and Springer have it placed in the Actinocrinidae as well as Actinocrinus,
Steganocrinus, Amphoracrinus, Physetocrinus, Teleiocrinus, and Strotocrinus. They
are all related, even though they can be quite different in appearance. It all has to do
with plate structure. "The lower brachials with well defined interbrachials between them,
forming an important part of the dorsal cup. Radials in contact except at the posterior side,
where they are separated by a hexagonal anal plate, which is followed by two interbrachials
without a second anal. Basals forming a hexagon." Wachsmuth and Springer, 1897. This
is their description for the Actinocrinidae. Now, if you explore the Cactocrinus in the
Burlington Formation, you will find that C. glans is the only species, as far as I know,
that occurs in the Upper Burlington. All the rest occur in the Lower Burlington. And many
species of Cactocrinus (from the Lower Burlington and elsewhere) have now been placed
in the genus Cusacrinus. But not Cactocrinus glans. Cactocrinus glans is still valid.

Doug DeRosear

Summary:
This specimen was collected from the Upper Burlington. Cactocrinus glans is restricted to
the Upper Burlington. Cactocrinus  from the Lower Burlington have a different appearance
because they are a different species.


Old Reference:
Missouri Geological Survey, Vol. IV (Part 1) 1894
By: Charles Rollin Keys, A. M., Ph.D.
Page 185 - Plate XXIV figure 2a and 2b

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Burlington Formation

Mississippian Fossils of Missouri