y L A T E X X X 1 Y 



Fig. I. CouMXARiA Ai.vKOi.AT A. Treiitoii group, St. Joseph's Island. 



2. alveolaris. Trenton group, Escanaba River. 



3. stellata. Hudson River group. Drummond's Island. 



4. alveolata. Trenton group, Dixon, Illinois. 



