358 Annals of the Carnegie Museum. 



The structure of the Potamogeton formation in this stage is : 



Fades. — 



Potamogeton pectinatus . 



Principal Species. — 



Potamogeton nutans, Naias flexilis, , 



Potamogeton loncJiitis, Utricularia vulgaris. 



Secondary Species. — 



Vallisneria spiralis, Philotria canadensis. 



The Nymphcea Formation. 



The Nymphcea formation occupies a zone outside of the Potamoge- 

 ton formation, in water from two to five feet in depth. It is not yet 

 well developed in this stage, but it is invading all three of the lagoons 

 associated with this stage. 



The structure of the formation as here developed is : 



Fades. — 



Nymphcea advena. 

 Principal Species. — 



Pontederia cor data. 



The Scirpus-Typha Formation. 



The Scirpus-Typha formation in Stage E extends from a few inches 

 above the water-level on the wet bank to a depth of about fourteen inches 

 below the water-level. Its structure is mainly the same as in Stage D, 

 but the Sabbatia-Litiicm formation surrounding it has been supplanted 

 by a formation, which, when once invasion has begun, rapidly gains 

 entire possession of the habitat, and, being very stable, is able to retain 

 possession for a comparatively long period. 



The Cladium-Calamagrostis Formation. 



The structure of this formation is here as follows : 

 Fades. — 



Cladium mariscoides, Calamagrostis canadensis. 



Priticipal Species. — 



Aster ericoides. 

 Secondary Species. — 



Asclepias incarnata, Hypericum boreale, 



Dryopteris thelypteris, Cyperus flavescens, 



Fquisetum hyemale. 



