INDIANA PALEONTOLOGY. I42. 



AOROCRINUS CASSEDAYI, Var. Charlestownensis. Rowley. 



Plate 41. Figs. 8, 9, 10, 11, 12, 13. 



This variety was figured and described in Part VIII of this publication 

 from a detached dorsal cup. As better specimens are now in our hands, we re- 

 figure and complete the description. 



The plates of the dorsal cup are strongly convex and present the appear- 

 ance of stellate nodes, the sutures being hidden in the deep interspaces. 



The rim formfed by the basal plates is less expanded than in A. cassedayl 

 and is strongly fluted, whereas it is smooth in Cassedayi . 



The first radial plates being as deep as the basal rim and their nodes almost 

 meeting the folds in the rim and the equal depths of the rest of the calyx plates 

 render the rim inconspicuous. 



The plate Yiodes all have a very crowded look. 



The third primary radials are much smaller than the first and second and 

 above them the two radials of the second series and the three of the third are 

 prominent and rounded, looking not unlike the pieces of free arms. 



The interradials are one large first, two large second and three small third 

 series pieces, the latter lying between the arm lobes. 



The anal plates are one, three, five. Above the anal fold or ridge is smooth 

 and further plates can not be made out. 



The anal opening is located latterly and one a distinct fold which extends 

 to the central dome spine. 



The plates of the ventral cup are small and quite strongly convex on the 

 ambulacral folds, those directly over the pairs of arm bases being spinose. 



There are twenty free arms and the openings are directed upward. 

 The central dome spine is strong but short. 

 The groups of arm bases are strongly lobed. 



In the drawings of the young specimen, figures 8, 9, 10, the artist has failed 

 to show the fluted character of the basal rim. 



The differences between the variety Chai'lestoionetisis and the species Cas- 

 sedayi, herein pointed out, are doubtless enough to separate the two forms spe- 

 cifically. If so, our crinoid will become Aorocn'nus Charlestownensis. 



Upper Devonian beds, near Charlestown, Ind. 



Collection of Mr. G. K. Greene. 



