8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 65 



1. Calyx reduced by the moving- inward of all the calyx plates, so 

 that they become closely appressed and, their longitudinal axes all 

 being parallel, form a closely knit column upon the summit of which 



the Visceral mass rests. Bathymetric Thermal 



range range 



Phrynocrinidse (Naumachocrinus) 508-703 38.1-40.0 



Bourgueticrinidas 62-2690 29.1-70.75 



2. Calyx reduced by the eversion and imbrication of the calyx 

 plates, so that eventually they come to form a platform composed of 

 superposed circlets of plates, all the plates in the same circlet lying 



in the Same plane. Bathymetric Thermal 



range range 



Pentacrinitidse CF-2900 28.7-80.0 



. Apiocrinidas 565-940 36.7-38.1 



Phrynocrinidse (Phrynocrinus) .. .508-703 38.1-40.0 



One type of calyx reduction consists in the calyx abruptly ceasing 

 growth upon reaching its perfected form, or, in the most extreme 

 cases, closing up after the manner of an umbrella, so that the visceral 

 mass, which continues to grow, is extruded and thus comes to lie, 

 entirely exposed laterally, upon the summit of a short column com- 

 posed of the much narrowed and more or less aligned calyx plates, 

 supported chiefly by the arm bases. 



But more commonly the reduction of the calyx plates takes the 

 course of a progressive retardation in their development whereby 

 they become smaller and smaller in relation to the lateral and dorsal 

 area of the visceral mass, the inner edges of the plates of each 

 circlet, as the circlets decrease in diameter, slipping inward over the 

 outer edges of the plates of the circlet next within. 



These two types of calyx reduction are, in a way, parallel to each 

 other; yet the first appears to be of a more primitive character than 

 the second, for the reason that the cessation of calyx growth and 

 development does not begin until after the calyx has reached its 

 perfected form, whereas in reduction by the second method the altera- 

 tion of the relation of the calyx plates begins, at least in the develop- 

 ing comatulids, in the very early stages before the elimination of the 

 radianal from the radial circlet. Thus it would appear logical to 

 derive the second type from the first by carrying the inhibition of the 

 formation of the calyx further back in the ontogeny or in the 

 phylogeny. 



