278 
Eliminating the highly variable organic matter and recalculating to 100''/^, the analyses 
assume the followinsj form ; 
Zygomctia micrihiiscus Chondrometra rugosa 
SiO., 0.05 0.06 
RjOj 0.62 0.27 
MgCO, 13.37 9-87 
CaCO, 85.48 89.80 
CajPjO, .... 0.48 Trace 
100.00 100.00 
The skeleton of Zygometra microdisctis contains the highest percentage of MgCOj of 
any of which analyses have been made. The percentage of MgCO., in the skeleton of Clio)idro- 
metra rugosa is what would be assumed from the temperature of its habitat. 
