Growth of Arachnoides placenta — Hines and Kenny 
235 
It would appear that the percentage increase 
in diameter during the second year is less for 
Arachnoides than for other echinoids. Those 
species inhabiting cooler waters apparently 
grow more rapidly than do the tropical A. 
placenta, but by the end of the third year 
Mellita, a warm water echinoid, and Arach- 
noides present a similar picture. 
The diameter-to-weight relationship for A. 
placenta approximates the expected cubic form 
and is similar to that expressed by Swan 
(1958) for Strongylocentrotus droehachiensis. 
However, the wide range of weight values for 
any one diameter makes it difficult to reduce 
the relationship to a series of separate equations 
as Swan (1958) has done for the Maine 
species. 
The authors wish to thank the members of 
the technical staff of the University College of 
Townsville who assisted in the collection of 
specimens for this study. 
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