31 



cuneiform projecting plates. In the ray on the right of the 

 azygous area the arms bifurcate on the fifth plate and the 

 branch adjoining the azygous area does not bifurcate again, 

 but the next one bifurcates on the ninth plate. The distal ray 

 bifurcates on the seventh plate and the proximal one does not 

 bifurcate. In other words, in this ray, one distal ray bifur- 

 cates and the ether does not, and one proximal ray bifurcates 

 and the other does not, which is an unusual method. In the 

 other three lateral rays the arms bifurcate on the sixth plate 

 and the distal arms bifurcate on the sixth, seventh and eighth 

 plates and the proximal arms do not bifurcate. This arrange- 

 ment gives to each of these four rays six arms. In the ray 

 opposite the azygous area the only bifurcation takes place on 

 the fifth plate, which gives to it two arms. There are, there- 

 fore, thirty-eight arms in this species. 



The first azygous plate rests on the sloping side of a subra- 

 dial and slightly truncates another below the first radial on the 

 right, and abuts the second and third azygous plates. The 

 second plate truncates a subradial and abuts the first radial on 

 the left and extends above the gaping suture. The third plate 

 truncates the first and extends nearly as high as the first arm 

 plate. Above these the plates are alternate as far as disclosed. 



This species is distinguished by its low calyx, thirty-eight 

 arms and rough angular aspect. It is one of the kind that has 

 been referred to Scaphiocrinus on account of the rough arms, 

 but it does not agree with that genus, in the structure of the 

 azygous area, but agrees with Poteriocrinus, to which genus we 

 refer it. We think it is not a Zeacrinus with which it has 

 some affinity. It cannot be mistaken for any other species. 



Found in the Keokuk Group, at Boonville, Missouri, and now 

 in the collection of F. A. Sampson. 



POTERIOCRINUS NEGLECT US, n. Sp. 



Plate IV, Fig. 3, side view, azygous area on ihe right; Fig. 4, 

 side view, azygous area on the left; Fig. 5, azygous 

 side; the specimen is laterally compressed, 

 as shown by the illustrations. 



Species medium or below medium size, constricted above the 

 first radials. Calyx short, cup- shaped. Plates slightly convex; 

 sutures distinct; surface granular. Column quite small. 



