BATOCEINID^. 389 



costals, and thence abrnptlj^ to the arm bases, which stand out horizontally, 

 forming a projecting rim. The radial plates are somewhat elevated or 

 rounded, while the other plates of the dorsal cup are flat and without orna- 

 mentation. Suture lines indistinct. 



Basal cup short, cylindrical, wider than the column, and very little con- 

 cave at the bottom. Radials twice as large as both costals together, their 

 upper faces concave. Costals of about equal size, transversely arranged; 

 the first quadrangular; the second pentangular. Distichals 2X10, resem- 

 bling the costals in form and size. Palmars 2X20 in the calyx; subquad- 

 rangular, and in contact laterally. Arm facets lunate, directed outward, 

 the respiratory pores small, and placed at the sides of the ambulacral 

 openings. Arms four to the ray, exceptionally two in the anterior one ; 

 they are very long, broadly paddle-shaped, and biserial from the second 

 free plate. To nearly two inches from the calyx, they are rather thin and 

 cylindrical, whence they grow perfectly flat, and increase rapidly to the 

 width of eight to nine mm., which is slightly reduced toward the extremities. 

 The flat portions are thickest along the median line, the sides being knife- 

 like with serrated edges, which turn slightly outward. At two-thirds their 

 height, the arms generally curve inward until their tips touch the calyx. 

 The proximal arm plates are quite short, but the plates increase to twice 

 their former length as they widen. Pinnules long, composed of long, flat 

 joints. Interradials, 1, 2, 1 ; the first very large, reaching the top of the 

 distichals. The anal plate is followed by three and two plates. Ventral 

 disk conical, somewhat bulging, often higher than the dorsal cup. The 

 plates are highly convex or conical, and of nearly uniform size. Anal tube 

 slightly excentric, rather short and slender. Column small. 



Horizon ami LocalUij. — Upper Burlington limestone, Burlington, Iowa. 



Types in the University Museum at Ann Arbor, Mich. 



.Se?7MrZ;s. — Professor Hall's description of this species is so indefinite 

 that little can be made out of it, and if it were not for his figures, which he 

 distributed privately among some of his colaborers eleven years later, the 

 species could not be distinguished from several others which occur in the 

 same locality. He gives the number of arms as sixteen ; stating, however, 

 that there were imperfections in his specimen. Either Hall described one 

 species and figured another, or the number of arms given is erroneous. 



