1885.] NATURAL SCIENCES OF PHILADELPHIA. 343 



form to identify even those elements which are so readily recog- 

 nized in other genera. 



In Acrocrinus Wortheni Wachsmuth, the comparatively large 

 basals are succeeded by a ring of twelve triangular plates, so 

 minute, however, that it requires a magnifier to discover them. 

 Another series of twelve larger plates constitutes the second 

 ring. These plates are joined by their lateral edges, their lower 

 angles resting between the preceding plates. Five of them have 

 a radial direction, seven are placed interradially, one opposite 

 each of the four regular interradial sides, three facing the anal 

 side. Ten of the plates are hexagonal ; only the middle one on 

 the az3'gous side, and the plate which is directed to the anterior 

 ra3 T , are heptagonal. The two latter plates have truncate upper 

 sides, which support, respectively, a vertical row of four very 

 similar hexagonal pieces ; one of them is interradial, and succeeded 

 by anal plates, the other strictly radial. 



The third ring consists of fourteen plates, larger than those of 

 the preceding one. They are not so regularly arranged, and more 

 variable in their size and form. Twelve of them alternate with 

 the plates of the second ring, while the other two rest upon the 

 truncate upper side of the heptagonal pieces just described. By 

 this arrangement (see diagram, PI. 9, fig. 1), the plate toward the 

 anterior ray is the only plate in this ring which has a radial posi- 

 tion, all others being located interradially, two to each of the four 

 regular interradial sides, four to the azygous side. 



The plates of the fourth ring differ considerably in form and 

 size, and their whole arrangement is irregular throughout. They 

 are sixteen in number, five radial in position, five directed to the 

 anal side, one to each side adjoining the anterior ray, and two to 

 each of the other two interradial sides. 



Above the fourth ring, the plates are readily recognized as 

 radials and interradials. In the specimen there are 2X5 radials, 

 and the interradials consist of three to each of the four regular 

 sides, and eight on the az} T gous side. The two radials connect 

 with the radial plates of the fourth ring only in the anterior ray, 

 in the four other rays they are separated from that ring by two 

 interradial pieces, which join underneath. 



In the original description of Acrocrinus Wortheni, the plates 

 of the fourth ring were included with the radials and interradials, 

 and the number of the former was given at three in the four 



