Carboniferous Rocks of the Mississippi Valleij. 317 



of the Keokuk limestone, Crawfordsville, Indiana. Cul' 

 lection of Wabash College. 



Forbesiocrinus Thiemei (n. s.). Body rapidly expand- 

 ing from the base to the free arms ; five prominent ridges 

 traversing its height along the rays ; base broadly trun- 

 cated. Basal and sub-radial plates very small, only the 

 outer ends of the latter projecting beyond the column, 

 leaving the middle of the bases of the first radials covered 

 by the column. Radial plates three in each series, grad- 

 ually increasing in width upwards ; the first and second 

 and sometimes the third plates of adjacent rays are united. 

 The first and third radial plates are sub-pentagonal ; the 

 second sub-quadrangular, the outer angles truncated by 

 the adjoining plates. The third radial supports on its up- 

 per sides the two main divisions of the ray, which again 

 divides on the third plate above. Beyond this the arms 

 are simple, and composed of a single series of very short 

 plates, strongly rounded on the back. Every third or 

 fourth plate in the lower and every second plate in the 

 upper part is much thickened and extended on the inner 

 side of the arm, supporting on its upper side an armlet, 

 which is composed of short, strong plates, large at base, 

 and rapidly diminishing towards the end. Arm joints 

 showing the small patelloid plates very distinctly. Surface 

 of plates of the first radial series strongly elevated in the 

 middle and depressed at the sides ; the last plate of the 

 first radial series and the last of the second radial series 

 bearing small pointed nodes. Interradial and anal plates 

 obsolete. Column proportionally large, composed of thin 

 plates. 



The absence of interradial and anal plates in this 

 species is a character not conformable with the genus 

 Forbesiocrinus. This, together with the rudimentary basal 

 and sub-radial plates, would seem to unite it as closely 

 with Ichthyocrinus; while the arm structure places it with 



