BATOCRINID^. - 433 



ing a single row of large distichals, and these the free arms, except in the 

 posterior rays, in which the plates facing the anal side are axillary, and give 

 off two arms, or three to those rays. Arms delicate ; composed of two rows 

 of rather long joints alternately arranged. Anal plate a little longer than 

 wide, contrary to the radials, which are wider than long ; it is followed by 

 three and one plate. The other interradii have but one interbrachial, above 

 which the distichals meet. Ventral disk highly convex, composed of but 

 few large plates, of which the orals occupy almost one half of the whole 

 surface. They are surrounded by five large radial plates, between which 

 are interposed two or three smaller interambulacral pieces. Anal tube 

 nearly central, very thin and short. 



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



Ti/2ie in the Illinois State collection. 



Dizygocrinus andrewsianus (MoChesnet). 

 Plate XXIX. Figs. 2a, h, c, d. 



I860. Actlnocrimcs andrewsianus — McChesney; New Palseoz. Poss.. p. 27. 

 1867. Actimcrinus andrewsianus — McChesney; Chicago Acad. Nat. Sci., p. 20, Plate 5, Kg. 5. 

 1881. Batocrinus andrewsianus — W. and Sp. ; Revision Palseocr., Part 11., p. 165 (Proceed. Acad. Nat. 

 Sci. Pliila., p. 339). 



A small species. Calyx obconical below the arms, the plates smooth and 

 almost flat; above the arms conical, and the plates convex, sometimes 

 tuberculous. 



Basal cup low saucer-shaped, the sides not projecting ; the column facet 

 •small, interbasal sutui'es indistinct. Radials of medium size, wider than long. 

 First costals small, quadrangular ; the second generally heptangular, a little 

 wider than the first, but not quite as long. Distichals two in all the rays ; 

 but in four of them the upper is axillary, and followed by a I'ow of palmars. 

 In the anterior ray, in which there are no palmars, the distichals are some- 

 what larger, and the second supports the arms. Arm-bearing plates slightly 

 projecting, in contact laterally except at the anal side. Arm openings 

 directed outward. Arms long, infolding, rather thin, not touching each 

 other laterally ; they are subcylindrical at their bases, somewhat flattened 

 and wider at the top. The anal plate, which is as large as the radials and 

 of a similar form, is followed by rows of 3, 3, and 2 plates, sometimes 

 with an additional piece in the arm regions. The interbrachials of the four 

 other sides consist of four plates in three rows. The plates of the ventral 

 disk are moderately large and of nearly the same size ; the anal tube is sub- 

 central, rather thin and short, not extending beyond the tips of the arms. 



