306 ERYLUS ROTUNDUS. 



DIMENSIONS OF ADULT ASPIDASTERS. 













E r y 1 u s 



rotund us 













var. 



megarhabda 



var. typica 



var. 

 cidaris 









A 



B 



o 



A 



B 



C 



D 



o 





«t-i 

 o 



Aspidasters 







average 

 rariety 





jcimen 



Jcimen 



from northeast Hawaii 



average; 

 ,'ariety 





averag 

 ies 







from South Molokai 



from Kauai 



limits and means of 

 all the forms of the ' 



from South Molokai 



from Kauai, dark sp< 



from Kauai, light sp< 



limits and means of 

 all the forms of the ^ 





limits and means of 

 the forms of the spec 





limits, n 



50-62 



53-66 



50-66 



65-77 



50-67 



60-72 



64-70 



50-77 



65-75 



50-77 



Lell<^(ll 



average of the 

 three largest, ji 



60 



64 



62 



72 



63 



71 



69 



68.8 



73 



67.4 



Breadth, limits, /< 



46-56 



49-59 



46-59 



54-68 



48-61 



57-70 



61-69 



48-70 



62-69 



46-70 



Tliieiviiess, limits, // 



6.2- 

 8.8 



4.6-5 



4.6- 

 8.8 



5-7.8 



5-6.4 



6-6.8 



4.4- 

 7.6 



4.4 

 7.8 



5-7 



4.4- 

 8.8 



A \ frage 



[iroportion of 



100: 



100: 



100: 



100: 



100: 



100: 



100: 



100: 



100: 



1()0: 



length 



to breadth to 



91: 



90: 



90.5: 



91: 



94: 



96: 



95: 



94: 



96: 



93.3 



thickness 



12.3 



8.2 



10.3 



9.7 



11.2 



9.8 



11.2 



10.5 



9.2 



10.2 



Thickness of piofnuliiig 

 rays, /t 



0.7- 

 1.6 



0.7- 

 1.7 



0.7- 

 1.7 



1-2 



0.8-1 



0.7-2 



1-1.9 



0.7-2 



0.7-1 



0.7-2 



The 3'oungest aspidasters observed were oval or circular discs, about half 

 the size of the adult, and composed of numerous, long, exceedingly slender, 

 perfectly straight rays, lying nearly in the same plane, and radiating from an 

 irregular, lobose structure 2-4 in diameter. This lobose centrum is appar- 

 ently composed of short, terminally rounded concentric rays, arising obliquely 

 to the plane occupied by the long rays. The rays, which in this young stage 

 appear to be isolated throughout, grow in length and in thickness. Their 

 longitudinal growth leads to an increase in the size of the aspidaster, their 

 transverse growth (thickening) to a coalescence of the rays themselves, which, 

 as the growth continues, progresses from the centre towards the margin of the 

 disc. Thus the aggregations of isolated, radial rays become larger, solid discs 

 with serrated margins. This goes on until the spicule has attained nearly its 

 full size. Then the longitudinal growth of the rays ceases, while their lateral 

 growth continues. This leads to a filling up of the serrations and to the forma- 



