RHODOCRINIDJE. ^ 223 



forming a circular pit, which is but i}artly filled by the upper joint of the 

 column. Plates without ornamentation^ a little convex^ the suture lines 

 slightly grooved. 



Infrabasals small, concealed by the column. Basals as large, or even 

 larger than the radials, their lower ends bending abruptly inward to take 

 part in the pit, the upper portions curving gently outward and upward. 

 Radials heptagonal, a little wider than long, and twice as large as the 

 costals, which are quite narrow. Distichals free from the first up ; the 

 upper faces of the latter slightly excavated to form the ambulacral opening. 

 The free distichals consist of about eight plates, which are very short; the 

 upper one axillary, supporting two arms, of which one branches again on 

 the eighth joint, while the other remains simple. Arms cylindrical, of nearly 

 uniform size, biserial above the last bifurcation ; the plates very short and 

 transversely arranged. Pinnules rather stout and in contact ; the joints 

 twice as long as wide, with deep ambulacral grooves. Interradial areas not 

 depressed ; arranged : 1, 2, 3, 2, succeeded by three or four more pieces. 

 The anal side has three plates in the second row. Yentral disk composed of 

 but few plates ; it is somewhat elevated at the margin, almost flat in the 

 middle. Orals well defined ; surrounded by two rows of rather large inter- 

 ambulacral pieces, which meet with the interbrachials. Anus subcentral, 

 opening through the disk. Column round ; axial canal small and stellate. 



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



Ty^e in the Museum of Comparative Zoology, Cambridge. 



Rhodocrinus Whitei Hall. 

 Flate XIII. Figs, la, h. e, and Plate XV. Figs. 6a, h. 



1861. Hall ; Description of New Spec. Criiioids, p. 9. 



1861. Hall; Bost. Journ. Nat. Hist., Vol. VII., p. 324. 



1872. Hall; N. Y. State Mus. Nat. Hist., Bull. I., Plate 6, Tigs. 19, 20, 21. 



1881. W. and Sp. ; Bevision Palgeocr., Part II., p. 213. 



Syn. Rhodocrinus Whitei, var. hurlingtonenns Hall ; 1861, Bost. Journ. Nat. Hist., Vol. YIL, p. 325. 



The largest known American species. Calyx depressed sub-globose, a 

 little wider than high ; the lower portion flattened and formed into a deep 

 concavity ; the sides decidedly bulging to the first costals, then contracting 

 to near the arm bases. All plates of the dorsal cup to the top of the cos- 

 tals of nearly the same size, all strongly convex, and without ornamentation. 



Infrabasals of medium size, slightly projecting beyond the column. Bas- 



