Upper Burlington Formation
Monroe County, Missouri
Click on picture to Magnify
originally placed in Actinocrinus
Actinocrinus glans (Hall, 1859) = Cactocrinus glans
I was puzzled by images illustrating Cactocrinus with a different appearance.
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.
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.
Missouri Geological Survey, Vol. IV (Part 1) 1894
By: Charles Rollin Keys, A. M., Ph.D.
Page 185 - Plate XXIV figure 2a and 2b
Mississippian Fossils of Missouri