61 



the regular areas, and four or five in the azygous area. Be- 

 sides, the ornamentation is different in the two species, and 

 the proboscis in that species is large and subcentral and the 

 arrangement of the plates on the vault is quite different in the 

 two species. But if the two-armed ray is normal then this is 

 a sixteen armed species so different from all other sixteen 

 armed species that have been described, that no comparison 

 with any of them is necessary. 



Found by Geo. K. Greene, in the Hamilton Group, near 

 Charlestown, Indiana, and now in the collection of Wm. F. E. 

 Gurley. 



Family POTERIOCRINIDJE. 



POTERIOCRINUS BLAIRI, n. Sp. 



Plate IV, Fig. 1, azygous view, ihe arms on the right a little 

 compressed; Fig. 2, view showing ihe ray opposite ihe 

 azygous area on the left, one of ihe arms 

 is spread out of place. 



Species medium size, robust, and having wide arms that fit 

 closely together as in Zeacrinus. Calyx obconoidal, nearly 

 twice as wide as high, truncated below for a rather large 

 column; sutures distinct; surface smooth. 



Basals very short, three or four times as wide as high. 

 Subradials wider than high, three haxagonal, and two hep- 

 tagonal; those adjoining the azygous area are heptagonal. 



First radials of unequal size, but about twice as wide as 

 high; truncated the entire width above and separated from the 

 first brachials or arm plates by a slightly gaping suture. The 

 second radials or brachials, as they are usually called, are of 

 unequal size and not uniform in shape. In four of the rays 

 these plates are wider than high, pentagonal and support 

 upon each upper sloping side the secondary radials or free 

 arms. The secondary radials are short, wide, quadrangular 

 and abut against each other. In one of the series, the fifth 

 plate is pentagonal, axillary and supports upon each upper 

 sloping side the tertiary radials; in the other series, preserved 

 in our specimen, the sixth plate is axillary, pentagonal and 

 supports on each upper sloping side the tertiary radials. No 

 further bifurcation is shown, though ten tertiary radials are 



