ERYLUS ROTUNDUS. 

 DIMENSIONS OF TRIAENES. 



301 



Ti'iaenes 



Erylus rotundus 



var. megarliabda 



var. typira 



var. 

 cidaris 



limits and means of averages of all 

 the forms of the species 



A 



B 



limits and means of averages of 

 all the forms of the variety 



A 



B 



C 



D 



limits and means of averages of 

 all the forms of the variety 



South Molokai 



'3 



w 



South Molokai 



Kauai, dark specimen 



Kauai, light specimen 



Northeast Hawaii 



Rliahdonio 



k'liglli (liin- 



it.s), /( 



170- 

 180 



350- 

 370 



170- 

 370 



200- 

 220 





200 





200- 

 220 



180- 

 190 



170- 

 370 



thickness 

 (limits), /! 



6-11 





6-11 



8-12 



8 



8-9 



8 



8-12 



7-8 



6-12 



Cladc-length (limits), // 



85- 

 180 



150- 

 200 



85- 

 200 



140- 

 225 



80- 

 210 



150- 

 220 



210- 

 250 



80- 

 250 



80- 

 270 



80- 

 270 



Cladome 

 breadth 



liinils, /( 



160- 

 290 



25t)- 

 350 



160- 

 350 



300- 

 360 



1.50- 

 400 



2.50- 

 350 



350- 

 390 



150- 

 400 



300- 

 440 



150- 

 440 



a\'erage of 

 the broadest 

 three, /( 



231 



333 



282 



347 



357 



310 



370 



346 



397 



335 



Clade-angle 



limits ° 



92- 

 102 





92- 

 102 



92- 

 107 





90 



90 



90- 

 107 



97- 

 104 



90- 

 107 



average ° 



96.5 





96.5 



99.5 





90 



90 



93.2 



100.5 



95.3 



The acanthhjlasters (Plate 6, figs. 14b, 15, 16; Plate 7, figs. 52-54b, 56b, 

 57b, 58, 59, 75b, 76b) have from two to fourteen concentric, regularly dis- 

 tributed rays. Two-rayed acanthtylasters are rare and have been observed 

 only in var. cidaris. Also the three-rayed, which have been found in var. 

 typica, form B, var. megarhabda, form A, and in var. cidaris, are not frequent. 

 Four- to eight-rayed acanthtylasters are abundant in all the forms. Acanthtyl- 

 asters with more than eight rays appear to be most frequent in var. typica, 

 form B, and in var. megarhabda, form A. The acanthtylasters measure 12-31 /( 

 in total diameter. Those of var. cidaris are somewhat smaller than those of the 

 other two varieties. The size of the acanthtylasters is on the whole in inverse 

 proportion to the number of their rays, those with from two to six rays being 

 16-31, those with from seven to nine rays 14-24, and those with from ten to 



