BAT0CRINIDJ5. 393 



has but two arms, and an additional distichal in place of the palmars. Arm 

 openings almost equidistant ; the space between the two posterior rays some- 

 what wider and more deeply grooved than those between the other rays ; 

 structure of the arms unknown. Interbrachials one and two, arched by the 

 palmars. Anal plate higher than the radials ; it supports three plates, of 

 which the middle one is the longest, and is followed by an elongate piece, 

 which rests between the palmars. Ventral disk shorter than the dorsal cup, 

 depressed conical ; the plates convex. Posterior oral central, three or four 

 times as large as any other plate of the tegnien, and strongly nodose. Anal 

 tube excentric and small. 



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



Tyfes in the collection of Wachsmuth and Springer. 



Eretmocrinus clio (Hall). 

 Plate XXXVI. Figs. 2a, h, and Plate XXXVII. Figs. 9a, I. 



1861. Adinocrinus clio — Hall ; Prelim. Descr. New Crinoids, p. 1, and Boston Joum. Nat. Hist., Vol. 



Vn., p. 262, Photogr. Plate 4, Fig. 7 (1S72, N. York State Bull. No. 1). 

 1881. Eretmocrinus clio — "W. and Sp. ; Revision Palseocr., Part II., p. 172. 



Considerably below medium size. Calyx a little higher than wide, grad- 

 ually and uniformly expanding from the base to the top of the distichals, 

 thence spreading somewhat more rapidly to the arm bases; ventral disk 

 depressed hemispherical, about one fifth shorter than the dorsal cup. Plates 

 from almost flat to moderately convex ; the first radials and anal plate a 

 little nodose. 



Base higher and narrower than usual in this genus ; slightly thickened at 

 the lower margins, and produced into a rim, which is rather deeply ex- 

 cavated at the bottom, and extends beyond the upper limits of the column. 

 Radials proportionally large, almost as long as wide, the lateral faces longer 

 than any of the others. First costals small, quadrangular, a little wider than 

 long. Second costals wider but not longer. Distichals one, large, axillary ; 

 supporting two ranges of palmars with four arms, except in the anterior ray 

 which has but two arms supported by two series of three distichals. Palmars 

 in contact laterally with one another and with the upper distichals of the 

 anterior ray, so as to form with them a continuous ring ; the arm-bearing 

 plates protruding, and rounded on the back. Ambulacral openings facing 

 outward, equidistant, except on the posterior side, where the interspace is 

 larger and slightly depressed. Arms long and incurving, slender and rounded 



.50 



