GEODIA ATAXASTRA. 



85 



ordinary amphiox forms with both ends sharp pointed. In var. angustana 

 these spicules are 120-200, mostly 160-200 n long and 3-5 fi thick; in var. 

 latana somewhat larger, 145-215 // long and 4-7 /i thick. The shorter ones are 

 on the whole thicker than the longer ones. In var. angustana the average 

 thickness of the minute rhabds less than 160 /( in length is 4.6 n, that of the 

 ones more than 160 in length 3.9 /t. 



The orthoplagiotriaenes (Plate 43, figs. 9-22, 24a, 27a) have a straight, 

 usually conical and sharp-pointed, rarely shortened, cylindrical, and terminally 

 rounded rhabdome. The ordinary pointed rhabdomes are, in var. angustana, 

 1.6-2.3, mostly 1.9-2.2 mm. long and, at the cladome, 29-70, mostly 40-60 

 thick, in var. latana they are considerably smaller, 1.3-1.7, mostly 1.5-1.6 mm. 

 long and 30-45, mostly 30-40 // thick. The cylindrical, terminally rounded 

 rhabdomes are as thick as the conical ones at the cladome but only 330 /i-lA 

 mm. long. 



I have studied the frequency of the different lengths of the ordinary pointed 

 orthoplagiotriaene-rhabdomes in a similar manner to the amphiox-lengths. 

 The curves representing the frequency of the different lengths measured are 

 here reproduced (Fig. B). 



Per cents of all 



rhabdomes 



measured. 



9o 



0 







1 — 



/ 

 / 

 ; 



I 













p 



/ 

 ; 



/ 















-TV 



/ 

 / 



; 



/ 



I 

 \ 

 1 















r - 

 / 



1 



1 



, 1 































i 













•V-n* >>>» 



s.^,;, vv'v'v v;^«vt^<VM mm. in length. 



Fig. B. Percentage frequency of lengths of rhabdomes of the orthoplagiotriaenes measured. 



Geodia ataxastra var. angustana. 



Geodia ataxastra var. latana. 



They are similar to the frequency-curves of the amphiox-lengths, and like 

 them exhibit a distinct main culmination, broad in var, latana and narrow in 



