CALYPTOCRINID^. 



331 







Fig. 15. 



Fig. 16. 



Fig. 14. 



Fig. 14, sliowing plates of tlie dorsal cup, the arms and their partitions. 



Fig. 15, the calyx in a side view. 



Fig. 16, the partition walls oi Bucalyptocrinus rosacens (after Schultze). 



b = basals ; 7^ = Eadials ; / = costals ; 11= distichals ; ibr = interbrachials ; id = interdistichals 

 A = arms ; irP = interradial partitions ; idP = interdistichal partitions ; tl = first ring of plates of the 

 tegmen ; iS = the second ring ; t8 = the third ring ; and t4 = the fourth or upper ring of the tegmen. 



plates limited to a certain number. The dorsal cup is perfectly pentamerous, 

 the rays being- separated by interbrachials of uniform number and size, and 

 their main divisions by a single large interdistichal. Still more important 

 from a classificatory point of view is the structure of the ventral disk, which 

 differs from that of any other known Crinoid, recent or fossil. It is com- 

 posed of only four rings of large plates of irregular form, of which the two 

 lower ones completely cover the disk ambulacra, which are subtegminal, the 

 upper ones forming a long neck or tube enclosing a narrow canal. Not 

 only do the plates of the disk, like those of the dorsal cup, consist of a defi- 

 nite number, but they are throughout this family unusually large, and their 

 arrangement does not appear to be. in accordance with the pentamerous 



