702 THE CEINOIDEA CAMERATA OF NORTH AMERICA. 



two palmars with two arms to the inner. Arms cylindrical, very stout for 

 the size of the species, and not tapering except at the tips ; their j^lates 

 short. Pinnules strong and closely set, the joints three to four times as long 

 as wide. Structure of the ventral disk unknov^n. 



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



2'ype destroyed in the great Chicago fire. 



Eemarhs. — The ornamentation of this species is very variable, as shown 

 by the illustrations. In some specimens the entire surface of the plates is 

 covered with small but distinct nodules, in others the nodules are confluent 

 and the surface appears to be coarsely granulated ; still others have irregu- 

 lar larger nodes at the median portion of the radials. The basal disk is also 

 flatter in some specimens than in others. 



Platycrinus Wortheni Hall. 

 Flate LXVII. Fig. 9. 



1858. Hall; Geol. Rep. Iowa, Vol. I., Part 11., p. 530, Plate 8, Pig. 4. 



1881. W. and Sp. ; Revision, PartH., p. 76 (Proceed. Acad. Nat. Soi. Phila,, p. 250). 



Of medium size. The species is of the type of P.perasjoer, and has a 

 similar ornamentation ; but the dorsal cup is more elongate, the nodes upon 

 the plates are less regular, and angular instead of rounded ; also the basal 

 disk is proportionally larger, the radials longer and more erect, and each 

 half of the rays has four to five arms instead of three. Dorsal cup cup-shaped, 

 angular alono; the interradial sutures, and truncate at the base : its whole 

 surface densely covered by prominent granules or subspiniform nodes. 



Basal disk concave ; sharply pentagonal; the extreme outer margins on a 

 level with the lower edges of the radials ; the proximal stem joints circular. 

 Eadials as long as wide at the upper end, subquadrangular, the lower faces 

 truncated, the sides very little expanding upwards. Facets wide and deep, 

 surrounded by a projecting rim, the upper margin broadly excavated. Basi- 

 radial and interradial sutures slightly grooved, the interbasal sutures obso- 

 lete. Costals small, trigonal, wider than long. Distichals short, more than 

 twice as wide as long, and the first, as well as the second, resting within the 

 facets, their inner faces suturally imited, as also those of the palmars. The 

 plates of the two succeeding orders of brachials are but slightly smaller than 

 the distichals, and the second plate of each order, as in the case of the dis- 

 tichals, is wider than the first. Arms eight to ten to the ray, rather stout. 



