692 THE CRINOIDEA CAMEKATA OF NORTH AMERICA. 



tichals small, twice as wide as long, placed obliquely, the two of the same 

 ray connected laterally. Second distichals considerably wider than the first, 

 but not longer. Palmars and pos1>palmars of the form of the distichals, 

 but somewhat smaller. Arms eight to the ray ; cylindrical, moderately 

 strong, biserial from the start; the upper edges of the plates forming a 

 small thickened ridge projecting over the lower margin of the succeed- 

 ing plate. Structure of ventral disk unknown. Column small for the size 

 of the s|)ecimens, elliptical and twisted ; the transverse articular ridge of 

 apposed faces prominent, with a distinct fossa at each side. 



Ho7-izon and Locality. — Lower Burlington limestone; Burlington, Iowa. 



T//pe in the (Worthen) Illinois State collection, Springfield. 



RemarJcs. — The ornamentation in some specimens is more conspicuous 

 than in others. The length of the radials and the depth of the basal cup 

 are also quite variable. The latter, however, may be understood by consid- 

 ering that the rows of nodes surrounding the margins of the plates repre- 

 sent lines of growth, and increased in number with age, and as the plates 

 grew faster longitudinally than horizontally, they became in the older speci- 

 mens proportionally longer. 



This species, with slight modifications, apparently occurred also at Lake 

 Valley, New Mexico. A specimen from that locality (Plate LXVIIL, Fig. 

 5) shows the structure of the ventral disk, which had not been observed in 

 any from Burlington, but as the arms are not preserved there is some doubt 

 as to its specific identity. It agrees with the Burlington specimens perfectly 

 in the ornamentation of the plates, but the second joint of the stem is de- 

 cidedly elliptic, the radials somewhat more convex, producing .slight angular 

 depressions at the basi-radial and interradial sutures, the upper angles of the 

 plates are more inflected, and the facets apparently a little deeper. The 

 ventral disk is depressed-hemispherical, decidedly flattened at the top, the 

 posterior side somewhat bulging, the orals comparative!}' small and very 

 slightly convex, the covering pieces tuberculous. There are but three inter- 

 ambulacral plates to each side, of which the middle one is extremely large, 

 and erect except that the upper end curves abruptly inward ; those of the 

 regular sides are subtrigonal in outline, but actually hexagonal; the anal 

 one wider, subquadrangular, and the top slightly excavated to form the 

 anal opening, which points upward. 



