MONOGRAPH OF THE EXISTING CRINOIDS. 



579 



The proportions of the longest columnals vary considerably; in general it 

 may be said that the more numerous the columnals the longer they are. The 

 relation of length to breadth in the longest columnals is shown in the following 

 table : 



Qlyptometra tuberosa 7:1 



Hathrometra prolixa 6:1 



Pramachocrinus kerguelensis 6:1 



Anthometra adriani 5:1 



Hathrometra tenella 4-5 :1 



fLamprometra protectus ' 4J :1 



Antedon bifida 4:1 



Hathrometra sarsii 4:1 



Comissia HttoraUs 4:1 



Cnmactinia meridionalis 3:1 



Beliometra glacialis 3-4:1 



Compsometra loveni 3:1 



Antedon petasus 3:1 



Crotalometra porrecta 2:1 



PtiJomctra mulleri 2:1 



Thauinatometra nutrix 1*:1 



From the figures it appears that, in general, the species belonging to the 

 Macrophreata have more numerous and longer columnals than those belonging to 

 the Oligophreata. 



The number of short discoidal or lenticular columnals following the centro- 

 dorsal shows considerable diversity, but the available figures are unsatisfactory 

 for comparative purposes. 



At first, when the column is increasing very rapidly in length, these columnals 

 are relatively few, usually only 1 or 2; just before the formation of the centro- 

 dorsal the number of new columnals formed beneath the calyx is continued as 

 before, but the development of these new columnals is greatly retarded; hence at 

 the time of the first appearance of the centrodorsal the number of short discoidal 

 or lenticular columnals at the summit of the column is relatively large. As the 

 centrodorsal grows the short columnals beneath it slowly increase in length, so that 

 at the time the animal is ready to discard the larval column the number of those still 

 discoidal or lenticular is usually reduced to 3, 2, or even 1. 



Most of the following figures are from specimens the exact comparative age 

 of which is unknown : 



Antedon petasus 



Anthometra adriani 5-7 



Promachocrinus kerguelensis 3-10 



Hathrometra prolixa 4-6 



Comissia littoralis 4-5 



Hathrometra tenella 3-6 



Compsometra loveni 4 



Hathrometra sarsii 3 



Thanmatomctra nutrix 3 



Heliometra glacialis 3 



Antedon biflda 2-3 



Antedon mediterranea 2-3 



Antedon adriatica 2-3 



frotalometra porrecta 1-3 



tLamprometra protectus 



rtilonietra mulleri 



Leptometra celtica 



Cnmactinia meridional-fa 



Glyptometra tnbcrosa 



2 

 2 



o 



1-2 



1 



No exact statement is possible, but the indications are that the short discoidal 

 or lenticular columnals are more numerous in the Macrophreata than in the Oligo- 

 phreata, as would be expected from the longer and more numerously jointed stems 

 of the former. 



