A Beginners Guide To Identifying Cincinnatian Crinoids

By Jack Kallmeyer

Camerata - Diplobathrida

Gaurocrinus nealli
Rhaphanocrinus sculptus

Crinoid Anatomical Glossary

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Gaurocrinus nealli


10 mm scale
Photos by Jack Kallmeyer
The cup of G. nealli has very prominent ray ridges that branch once on the calyx and at least one more time above it.  The anal series is a raised ridge along the side of the calyxGaurocrinus is a diplobathrid camerate crinoid meaning that the cup is composed of three levels of plates.  The calyx plates between the raised ridges are small and irregularly shaped. The arms are pinnulate. The tegmen which covers the top of the calyx is comprised of many small plates with a small, narrow, dome-shaped anal sac.

The stems are pentagonal in shape and vary in diameter depending upon position. See stem descriptions for details.
 
Gaurocrinus used a distally coiled stem type of holdfast.

Gaurocrinus can be found in the upper Waynesville (Blanchester Member) and lower Liberty Formations.


Gaurocrinus Stems
10 mm scale
Photo and Artwork by Jack Kallmeyer

Stem is pentagonal with very rounded corners. On some columnals the corners project more than in this drawing but remain rounded. The articulating ridges are always perpendicular to the sides of the pentagon. The central opening is rounded pentagonal.

Rhaphanocrinus sculptus


(#1) Note the two juvenile cups on the upper left side of the larger crinoid.
5 mm scale (#1), 10 mm scale (#2)

Photos by Jack Kallmeyer

5 mm scale
Photo by Jack Kallmeyer


This ornate crinoid is rare.  Miami University, the Field Museum and the Smithsonian seem to be the only institutions that have any at all and they only have five between them.  These crinoids have been found in the upper Waynesville and lower Liberty Formations.

Rhaphanocrinus was originally mis-classified as a Glyptocrinus (a monobathrid camerate) because it seemed to have only two levels of plates composing the cup.  It was later re-described when the third level of plates (lowest) was found to be present but hidden by the basal plates above them.  When you see this crinoid you will see how easy it is to make that error.  The basal plates (the middle level) project out over the stem with spectacular ridges that hide the lower infrabasals.

The most obvious features of R. sculptus are the very high narrow ray ridges that begin at the basal plates.  These ridges stand out sharply away from the calyx as if they were knife blades.  The plates between the ray ridges also have smaller ridges.  The adult crowns do not have an anal ridge on the side of the calyx.  The tegmen is composed of many tiny plates.  The heavy ornamentation on the calyx is missing from the smallest individuals so that there is a gradation of ornamentation from the smallest to the largest individuals.

The arms of Rhaphanocrinus are round and carry pinnules.


Photo 10 mm scale
Photo and artwork by Jack Kallmeyer

The external shape of the stem can be described as broadly pentalobate with the diameter varying with position along the stem.  Columnals nearest to the cup are more circular as are the smallest diameter columnals. The articulating ridges are radially arranged in a narrow ring.  The central opening is circular.


Rhaphanocrinus
 used a distally coiled stem type of holdfast.
5 mm scale
Photo by Jack Kallmeyer

 

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