448 THE DKPTIJS OF THE SKA. [CHAP. ix. 



calcareous laminae, clinging to small pieces of shell, 

 grains of sand anything which may improve the 



anchorage of the crinoid in the soft mud which is 



' 



nearly universal at great depths. 



In Ehizocrinus the basal series of plates of the 

 cup are not distinguishable. They are masked in 

 a closed ring at the top of the stem; and whether 

 the ring be composed of the fused basals alone, or 

 of an upper stem-joint with the basals within it 

 forming a ( rosette/ as in the calyx of Antedon, is 

 a question which can only be solved by a careful 

 tracing of successive stages of development. The 

 first radials are likewise fused, and form the upper 

 wider portion of the funnel-shaped calyx. The first 

 radials are deeply excavated above for the insertion 

 of the muscles and ligaments which unite them to 

 the second radials by a true (or moveable) joint. 

 One of the most remarkable points in connection 

 with this species is, that the first radials the first 

 joints of the arm are variable in number, some 

 examples having four rays, some five, some six, and 

 a very small number seven, in the following pro 

 portions. Out of seventy-five specimens examined 

 by Sars, there were 



15 with 4 arms. 



43 5 



15 6 



2 7 



This variability in so important a character, par 

 ticularly when associated with so great a prepon 

 derance in bulk of the vegetative over the more 

 specially animal parts of the organism, must un 

 doubtedly be accepted as indicating a deterioration 



