6504 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
wide and rather deep notch. Facets occupying half the width of the 
plates, semi-circular, only excavated at their outer faces, the inner edges 
| of the plates being in a straight line, which is slightly notched for the 
| passage of the ambulacral vessels. Costals moderately large, sub-pentagonal; 
a 
ti) their lateral margins very short, directed outward and slightly upward. Dis- 
y | tichals and palmars once and a half as wide as long, the former giving off 
HI} an arm to one side, and two palmars to the other, the latter two arms, 
making three arms to each subdivision, or six arms to the ray. Arms rather 
slender, very slightly tapering, rounded on the back, their five or six prox- 
i | imal plates wedge-form and uniserial, the succeeding ones biserial. The 
) arm plates are nearly as long as wide, and each one is marked by a small, 
i transverse elevation projecting from the sides of the arms. Pinnules nearly, 
| i or quite, in contact laterally. 
| | Ventral disk depressed hemispherical; orals large, tuberculous, excen- 
Wa BT tric, and asymmetrically arranged ; disk ambulacra short and- composed of 
Ht i few rather large pieces. The interambulacrals consist of a single row of 
il three plates, of which the two at the sides are very narrow and bend 
He i i| | abruptly outward; the middle one large, and resting invariably against the 
‘iE orals. The middle plate of the anal side, which is larger and sub-quadrangu- 
AM 
a lar, is followed by two medium sized plates, and these by numerous smaller 
we | ones, which together form an elongate protuberance or short anal tube, 5 to 
} i i | 6 mm. in length, directed upward, and curving slightly inward to the middle 
‘| 
| 1 of the disk ; its lower margin, bordering the posterior oral, slightly truncat- 
i ing its outer edge. Column moderately twisted, the joints decidedly elliptic 
i) en in the adult, almost circular in young specimens. 
i 
| . 
yi | Florizon and Locality. — Lower Burlington limestone, Burlington, Iowa; 
) | and found at the same horizon throughout Missouri, and in Southwestern 
1 " New Mexico. 2 
| i), a3 ' femarks. — The subglobose form of the calyx, but still more the con- | 
| | struction of the ventral disk with its incurving anal tube and the large 
ain) interambulacral plates which invariably touch the orals, distinguish this 
species from all others known to us. 
Ht In describing this species we had for comparison over sixty specimens of 
all sizes, from 12 mm., including arms, to 8 em., showing the modifications 
i] | that took place in the growing Crinoid, in the form of the calyx and the 
| 
| 
Hy structure of the arms. The calyx of young specimens is shorter, the base 
Nin ns ZI 
NM eal more depressed, the arms zigzag, and composed of long wedge-form plates, 
