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ANNALS NEW YORK ACADEMY OF SCIENCES 
position is distinctly marked. Figure 20c, a still later stage, shows the cardi¬ 
nal septum very short and the fossula distinctly marked and bulging in 
appearance, while the secondary septa on either side are crowded away from 
the median line. The appearance of the tertiary septa is distinctly marked 
Fig. 20. Heterophrentis prolijica. X 4. 
in this section, although calcification has continued until they are united 
throughout their length with the secondary septa. Their presence and 
position is indicated in the figure by the dark central line of calcification. 
In figure 20d, cut from the base of the cup, the adult condition is shown. 
