A MONOGRAPH OF THE EXISTING CRINOIDS 403 



Diagnostic features. The longest cirrus segments are but little longer than broad, 

 and the distal cirrus segments are twice as broad as long or even broader; the proximal 

 pinnules are less enlarged than are those of 0. erinacea and, though more or less 

 stiffened basally and moderately elongated, they are flexible distally; there are 40^4 

 arms 90-140 mm. long; and the cirri have 41-80 segments. 



Description. The centrodorsal is hemispherical and is more or less completely 

 covered with cirrus sockets. 



The cirri are composed of 60-80 segments and may reach a length of 60 mm. In 

 the proximal portion of the cirri the segments, except for a few of the basal ones, are 

 usually slightly longer than broad; the remaining segments become gradually slightly 

 shorter. At a variable distance from the base of the cirri the distal dorsal edge of the 

 segments begins to project and later develops a sharp spine that retains its distal 

 position on the segment almost to the end of the cirri but here passes back more 

 toward the middle. 



The radials are more or less completely, and sometimes wholly, visible. Their 

 dorsal surface is approximately parallel with the dorsoventral axis of the animal. The 

 IBn are incompletely united laterally; they are as long as the free sides of the rather 

 large and pentagonal IBr 2 (axillaries). The postradial series as a rule divide three 

 tunes. Individual IVBr series may be present. All the division series are 2. The 

 IVBr series, if present, occur always on the inner side of the inner IIIBr axillaries. 

 The articulations between the elements of the division series are tubercular. The 

 post-radial series from the IBr t to the IIIBr axillaries often have their outer side more 

 or less strongly produced into a shelflike border with sharp edges and a flattened outer 

 side, but the thickening of the ventrolateral edges of the individual ossicles collectively 

 forming this border may be discontinuous without any flattening. In other cases the 

 production of the outer sides of the postradial series may be lacking altogether, their 

 outer sides being entirely smooth. When their lateral edges are strongly produced 

 the post-radial series are almost in lateral contact, otherwise they are well separated. 



There are 40, or a few more, arms 140 mm. long. The arms are long, smooth, 

 and rather slender, with the dorsal surface strongly rounded. The lowest brachials 

 may have flattened sides. The first brachials are entirely, or only partially, united 

 interiorly. They are somewhat shorter than the second brachials, which are approxi- 

 mately square. The first syzygial pair (composed of brachials 3+4) is markedly 

 longer than broad. This is succeeded by six to nine more or less discoidal brachials, 

 which bear a small lateral produced point, alternating in position on succeeding brachi- 

 als, on their proximal borders. On their distal borders they sometimes bear a similar 

 small sharp process. These are followed by a series of rather short triangular bra- 

 chials, which before the middle of the arm pass over into bluntly wedge-shaped bra- 

 chials. Toward the end of the arms the brachials become more square. The triangu- 

 lar and bluntly wedge-shaped brachials have on their distal edge a sharp production 

 laterally placed and alternating in position on succeeding brachials. 



The first syzygy is between brachials 3+4, the second is from the thirty -ninth to 

 the forty-sixth brachial, and the distal intersyzygial interval is from 4 to 21, often 

 from 5 to 10, muscular articulations. 



