24 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



ARACE^3. 



Arum family. 



Acorus calamus, L. — Sweet Flag. Calamus. 

 Common. 



LEMNACE^]. 



Duckweed family. 



Lemna trisulca, L.— Duckweed. Duck's-rneat. 



Widely diffused. 

 Lemna minor, L. 



America and Europe. 

 Lemna gibba, L. 



Chiefly in Europe, but has been found in Arizona. 



TYPHACE^E. 



Cat-tail family. 



Typlia latifolia, L. — Cat-tail Flag. 



Very common. 

 Typlia angustifolia, L. — Narrow-leaved Cat-tail. 



Less common, but found in this District and notably in a pond near 

 the foot of Eighteenth street. 



NAIADACE.E. 



Pond-weed family. 



Potamogeton natans, L. — Pondweed. 



Common. 



ALISMACE^E. 



Water-Plantain family. 



Alisma natans, L. — Water-Plantain. 



Europe, Siberia. 

 Sagittaria variabilis, var. latifolia, Eng. (Sagittaria latifolia, Willd.). — 

 Arrowhead. 



Common. 

 Butomus umbellatus, L. 



Europe; Northern Asia. 



HYDROCHAEIDACE^E. 



Frog's-bit family. 



Anacharis Canadensis, Planchon. {Elodea Canadensis, Michx.). — Water- 

 weed. 



Common. 

 Vallisneria spiralis, L. — Tape-grass; Eel-grass. 



Common. 



