1881.] NATURAL SCIENCES OF PHILADELPHIA. 315 



Generic Diagnosis Body turbinate, more or less lobed at the 



arm-regions ; calyx beautifully ornamented with radiating striae, 

 which concentrate at the middle of the plate, where they form 

 into a more or less prominent node ; vault extended into a large 

 subcentral anal tube. 



Basals three, equal, rather large, and forming a shallow cup, the 

 lower side slightly excavated for the column. Primarj'^ radials 

 3X5, the first larger than the rest, alternately hexagonal and 

 heptagonal, generally higBer than wide ; the second hexagonal, 

 smaller than the first, its height almost as great as its width ; the 

 third pentagonal and smaller, frequently bent outward, sometimes 

 abruptl}^ and forming the base of a lateral extension, which gives 

 to the radial portions a lobed, and to the general body a stellate 

 form. Secondary radials 1 X 10, axillary. Succeeding orders of 

 radials composed of a single series of plates to each division of 

 the ray, the one axillary, the other simple. The simple plate is 

 succeeded by a number of brachials connected with the body, 

 which jointly form a fixed branch in a lateral direction. 



The axillary plate supports always toward the opposite side of 

 the preceding order the next series of radials, and so on alter- 

 nately until the full number of arms of the species is produced. 

 Arms numerous, not bifurcating in their free state, or rarely so ; 

 their number very variable, ranging among the different species 

 from not less than twenty to fifty or more ; and these equally 

 divided among the rays. The arms are long, rather heavy, their 

 upper ends round or somewhat flattened, the tips infolded. The}'^ 

 are composed of a double series of narrow plates, separated by a 

 zigzag suture. The pinnules are long, given off, like in the case of 

 all double-jointed arms, from every joint and from both rows, they 

 are laterally compressed, with the abutting sides flat. The joints of 

 which the pinnules are composed are long, and they are provided 

 at their outer side, near the middle, with a tooth-like spine, some- 

 times of considerable length, which is curved upward in form of 

 a hook. The inner side of the joints is deeply grooved, and 

 covered with two rows of small alternate plates. The pinnules 

 are laterally attached, and resemble a fine network ; those of the 

 same arm rest tightly against those of the opposite row, thus 

 closing the ventral furrows both of arm and pinnules, in case the 

 arms are folded. 



The interradials generally consist of three large plates, almost 



