286 New Species of Crinoidea from the 



Second radial or sub-bracliial plates small, sub-pentagonal, 

 giving origin to an arm on each of the two upper sides ; 

 one of these is simple, and one bifurcates on the second 

 plate above, giving three arms to the ray. 



Anns composed of a single scries of plates at base, be- 

 coming gradually double towards the upper part. Tentac- 

 ula long, composed of long and comparatively strong 

 joints. Surface of plates entirely covered with small ele- 

 vated pustules. Column strong, composed of unequal, 

 somewhat angularly elliptical plates, so arranged as to give 

 the column a twisted appearance. 



The form of the radial plates and the surface markings 

 distinguish this species from every other in these rocks. 



Geological formation and locality. Burlington lime- 

 stone, Burlington, Iowa. 



Platycrinus excavatus (n. s.). Body discoid to the arm 

 bases. Basal plates deeply impressed, forming a conical 

 or funnel-shaped cavity. First radial plates sub-quadran- 

 gular, rapidly expanding to their upper edges, which are 

 more than twice as wide as the lower. Articulating scar 

 extending less than half the width of the plate, occupied 

 by the small, sub-triangular, sub-brachial plate, and the first 

 arm plate on each side. 



Summit and arms unknown. 



The suture lines of the first radial plates are profoundly 

 grooved or cliannelled, with an elevated, thickened ridge 

 extending along the lateral and basal margins, while the 

 intermediate space is slightly concave, without other sur- 

 face markings. 



The surface characters of this species are so peculiar 

 that they distinguish it from every other species known 

 to me. 



Geological formation and locality. Burlington lime- 

 stone, Burlington, Iowa. 



Platycrinus hrcvinodus (n. s.). Body broadly cup-shaped, 



