198 -D- Echinodermata. 



vex, in form of a ten-rayed star, indistinctly grooved between the arm bases. 

 Vault constructed of larger and smaller pieces, which all decrease outward. The 

 larger ones, which include the apical and all radial plates, are nodose or in part 

 spiniferous ; the smaller ones , including interradial and other accessory pieces 

 are scarcely convex. The inner floor of the vault is strengthened by braces, which 

 increase in thickness as they recede from the centre, and which, on approaching 

 the rim, extend to the calyx, and form tunneled passages, one to each arm ope- 

 ning. Column comparatively slender, composed of short, round joints, a part of 

 which, at regular intervals, project out beyond the others, and send up and down, 

 all around, at equal distances, five thickened processes or ribs, apparently as a 

 natural provision to give it strength without destroying its flexibility. These pro- 

 cesses give to the column a highly sculptured and somewhat pentagonal aspect, 

 especially in its upper portions, where they are prominent and almost continuous 

 vertically. But as these processes are only attached to the older and larger joints 

 of the column, they gradually grow farther apart as they recede from the body, 

 by the interpolation of the later developed joints, which increase in number 

 downward. Some species, in place of five, have ten or more rows of processes 

 along the column. Perforation of medium size: pentalobate." 



Gennaeocrinus nov. gen. (subfarn. Actinocrinidae). General form of the body 

 wider than high , lobed at the arm regions ; calyx beautifully striated , the 

 higher radials formed into ridges and resembling fixed arms; vault low 

 hemispherical, composed of small, spiuerous or nodose plates. Basals three, 

 short, with a tripartite rim formed by the projection of the lower margin of 

 the plates. Primary radials 3X5, of nearly similar form but decreasing in 

 size upward. The third radials gives off IX 10 secondary radials, and these 

 form the two main trunks, of which each one gives off, alternately through- 

 out all the bifurcations, and from every first joint, an axillary, and to the oppo- 

 site side a fixed arm plate, the one supporting the next order of radials, the other 

 being succeeded by additional arm plates, which on becoming free, pass into a 

 simple arm. Interradials numerous, from five to seven or more, the second rest- 

 ing between the second and third primary radials, the upper ones being in con- 

 tact with the interradial plates. The space between the rays is wide, deeply de- 

 pressed , especially at the posterior side, and this depression extends to the 

 vault. Anal area very wide, the first plate in line with the first radials, and of 

 their size. There are two plates in the second range, three or four in the third, 

 with a large number of small pieces above, which imperceptibly connect with the 

 plates of the vault. Interaxillary plates one to three. Vault depressed, its radial 

 portions formed into ridges or lobes , which rapidly increase in prominence to- 

 ward the arm regions. It is composed of moderately small, apparently irregularly 

 arranged pieces, which are more or less spiniferous. Anus excentric, probably in 

 form of a simple opening through the vault. Arms unknown. 



Centrocrinus Wachsm. &Spr. nov. subgen. (gen. Macros tyloer inns Hall., subfarn. Acti- 

 nocrinidae) . Calyx subcylindrical ; symmetry perfectly pentahedral ; the principal 

 plates produced into spines ; the calyx in its lower portions almost resembling Pla- 

 tycrinus, owing to the form and size of basals and first radials. Basal disk large, 

 pentagonal, composed of three unequal pieces, two of them pentangular, and twice 

 the size of the third, which is quadrangular. Primary radials 3X5; the first 

 very large and spiniferous ; second radials much smaller than the first, short and 

 quadrangular or nearly so ; third radials pentangular, sometimes triangular, as 

 short as - - and occasionally narrower - than the second. Secondary radials 

 1X10, bent abruptly outward and supporting the arms. There are. so far as 

 known , two arms to each ray. Interradials four to five: the first large and fre- 



