PROCEEDINGS OF THE UNITED STATES NATIONAL MUSEUM 
tssued 4. 
SMITHSONIAN INSTITUTION 
U. S. NATIONAL MUSEUM 
Vol. 92 Washington: 1942 No. 3144 
RHOPOCRINUS, A NEW FOSSIL INADUNATE CRINOID 
GENUS 
By Epwin Kix 
The new crinoid genus here described ranges from the St. Louis 
(or perhaps Ste. Genevieve) well up into the Chester group. Speci-— 
mens have been found in Illinois, Tennessee, Alabama, and Ken- 
tucky. One new species and two described species are referred to 
the genus. In addition two new species are known. A new family 
is proposed for the reception of this and certain other Mississippian 
genera : 
PACHYLOCRINIDAE, new family 
Crown compact and as a rule comparatively low. Dorsal cup 
broadly turbinate to basin-shaped. Three anal plates in cup. Ven- 
tral sac composed of numerous vertical rows of small plates. Sac 
reflexed. Arms isotomous in early forms, evolving through stages 
of endotomy to parendotomy. J/&r, two, but variation is possible in 
ant FR. Column pentagonal in early forms, becoming circular in 
section in later phylogenetic development. 
Contained genera.—Pachylocrinus, Rhopocrinus, Hylodecrinus. 
Remarks —This family is segregated from the amorphous group 
commonly designated as Poteriocrinidae. More exactly, it repre- 
sents a part of the family Scaphiocrinidae as conceived by Bather. 
Scaphiocrinus is a synonym or close ally of Graphiocrinus, and Bather 
in making the family was laboring under a misapprehension as to 
the real nature of the genus. I am elsewhere proposing the family 
Zeacrinidae for some of the structural types included by Bather 
in his Scaphiocrinidae, and the Pachylocrinidae will take care of part 
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