EXPLANATION TO PLATE XXV. 



Fie. 1. Sertularella dentifera Torrey. Part of colony (enlarged). (After Torrey.) 



2. Scrtnldn'Ilii i/enlij'i'r/i. Two hydrothecse, showing reduplicated margin? (enlarfteil). (After Torrey.) 



3. Serlularella tj^euspidaia (Alder). Part of colony (enlarged). 



4, 5. Sertrdarella iricuspidata. Gonangia (enlarged). 



it. Sertularella tricuspidata ( large form from Alaska). Part of colony (enlarged). 

 7. Xi-rhiliii'i'llit Iriruxjiidiitii. Single hydrotheca (greatly enlarged). 



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