PLAXrCRINID^. 673 



across the arm ; in the iipjDer [lower] part the arm plates are proportionally 

 longer, and extend entirely across, but separating very slightly the two 

 adjacent plates on the opposite side, making a single range of plates, with 

 their longer faces alternately on opposite sides." This is exactly the con- 

 dition of the arms in every young Flatycrinus when it enters the biserial 

 stage. 



Flatycrinus Sampsoni S. A. Miller. 

 Plate LXX. Fig. 10. 



1891. S. A. Miller; Geol. Surv. Missouri, Bull. 4, p. 13, Plate 1, Fig. 11. 



A large species of a very unusual form. Dorsal cup cylindrical almost 

 throughout its full length, perhaps a little narrower at the upper end ; the 

 base broadly truncated. Plates thin and smooth, the suture lines very 

 slightly grooved. The basal cup resembles a very low disk with nearly 

 erect sides; it is very broadly truncated at the bottom, the sides slightly 

 expanding ; the upper faces form an almost straight line around the cup, 

 the angles being so obscure as to be scarcely perceptible ; height of the cup 

 equal to a little more than one third the length of the radials ; the inter- 

 basal suture lines barely visible. Eadials of imequal size, some of them 

 much wider than others, the widest ones about once and a half as wide as. 

 long, the narrow ones almost twice as long as wide ; the sides parallel. 

 Facets sun-ounded by a projecting rim ; they are narrow, moderately deep, 

 and directed upwards. All other parts unknown. 



Horizon and Locality. — Upper Burlington limestone, Burlington, Iowa, 

 and Sedalia, Mo. 



Type in the collection of Mr. Sampson. 



Bemarks. — Described by Miller from a natural cast, but the species is so 

 remarkable that it is readily identified. We possess of it a nearly perfect 

 dorsal cup from which our description was made. 



