58 OWEN AND SHUMARD'S FOSSIL CRINOIDEA. 



of the genus with which we are acquainted : a specimen from Burlington, though 

 devoid of the abdominal plates, is nearly two inches in diameter. 



Platycrinus Yandellii. (New sp.) 



PI. 7, fig. 6, a, h. 



Basal plate. — Somewhat massive, pentagonal, flattened and rather deeply excavated 

 at the point where the supra-columnar joint is attached ; with a minute perforation 

 in the centre corresponding to the canal in the column. The surface is embellished 

 with very prominent tubercles usually arranged in a single series, just within, and 

 parallel to, the outer borders of the plate. 



The superior plates are five ; broad, sub-hexagonal, and spreading towards the 

 superior edges. The surface of each plate, like that of the basal plate, is studded 

 with highly raised tubercles ; in some specimens these are disposed with great 

 regularity in ranges parallel to the lateral and inferior edges ; in others they are 

 scattered irregularly over the plate. The excavations for the attachment of the arms 

 are wide, shallow, and somewhat reniform. Each excavation is striated on the 

 margin, and crossed near the middle by a transverse ridge serving to prevent 

 displacement of the arms. 



The column and arms have not been discovered. 



Dimensions. — Height of cup 4 lines, breadth 1\ lines, height of superior plates 4 

 lines, breadth of do. 5 lines. This encrinite is nearly related to Platycrinus 

 rugosus and P. tuberculatiis of Miller, but is separated from those species by the more 

 depressed form of the cup, the greater proportionate breadth of the superior plates, 

 and the larger articulating surface for the arms. 



Formation and Locality. — It occurs with the preceding species in the sub- 

 carboniferous limestone at Burlington, Iowa. We have likewise discovered it near 

 Salem, Indiana, holding a similar geological position. It affords us much pleasure, 

 as a slight tribute of respect and esteem, to dedicate this beautiful species to our 

 friend Professor L. P. Yandell, of Louisville, Kentucky. 



Platycrinus discoideus. (New sp.) 



PL 7, fig. 1, «, h. 



The general outline of the cup of this species is that of a decagon ; and the visceral 

 cavity is proportionally more shallow than in any of the hitherto described species of 

 this genus, the diameter being about one inch, while the height is not quite three lines. 



Basal plate pentagonal, massive, concave towards the centre and bordered near 

 the margin by an uneven ridge. The circle of attachment for the column is 

 moderately large and finely striated. The margins of the plate are bevelled. 



