Wood— Crinoid from the Hamilton of Charlestown , Tad. 299 



The whorl of crescentic ridges on the radials when viewed 

 from below bears some resemblance to a six-petaled flower. 

 Each of three alternate petals has a small erect spine at the 

 center. 



The carina following the median line of the ray and its 

 branches is stronger than the others and increases in promi- 

 nence from the radials to the arm bases. This carina is straight 

 to a point above the middle of the second costal, where it 

 divides, each branch crossing a distichal and branching again 

 below the upper angle of the plate. A third branching takes 

 place on the inner primary palmar. 



Spines are an important feature of the surface ornamenta- 

 tion. In addition to those already mentioned there are often 

 minute spines in the angle formed by the finer and coarser 

 carina of the brachials and interbrachials. These are some- 

 times elongated, showing a tendency to form a new carina in 

 this position. The second costal bears a very small spine in 

 the angle formed by the branching of the strong carina, and 

 two similar spines are present on the inner side of the dis- 

 tichal below the branching and in line with the straight por- 

 tion of the carina. Three much larger spines, decreasing in 

 size upward, are present on the interpalmars, one at the center 

 of each plate. 



The upper plates of the calyx are somewhat variable in 

 shape. The second costals of the postero-lateral rays are hep- 

 tagonal, those of the anterolateral rays pentagonal and the 

 anterior second costal is hexagonal, having three edges on one 

 side, above the base, and two on the other ; that is, one repre- 

 sents the heptagonal and the other the pentagonal type of 

 plate. The distichals also vary in shape in the different rays. 

 Those resting upon heptagonal costals have six and those on 

 pentagonal costals seven sides. The distichal on one side of 

 the anterior ray is thus heptagonal and that on the other side 

 hexagonal, corresponding with the irregularity of the adjacent 

 costal. The primary palmars resting upon the distichals are 

 heptagonal on the inner and pentagonal on the outer side of 

 the ray. The first interpalmar is an inverted pentagonal plate, 

 the second hexagonal and the third obscurely pentagonal. 



The first interbrachial is in each case regularly hexagonal y 

 but the interbrachials of the second row are six or seven-sided 

 according to the heptagonal or pentagonal shape of the adjoin- 

 ing second costal. The middle plate of the third row is hexa- 

 gonal, wider at the lower than at the upper end. The other 

 two plates of this row are hexagonal when the nearest dis- 

 tichal has the same number of sides and five-sided when the 

 latter is a heptagonal plate. 



