No. 2.] FRESH-WATER PROTOZOA. I9 



at the end. Skeleton a silicious shell nearly spherical, con- 

 taining numerous round or polygonal openings. Attached 

 by a long, tubular stock, whose root-like base is fastened 

 to other objects. The young shell colorless, but later 

 brown. The animal moves freely in its shell by means of 

 its pjeudopodia. 

 Clath. elegans Cienk., Fig. 28. 



CLASS MASTIGOPHORA. 



The classification of the Mastigophora adopted below is 

 essentially that of Biitschli. It does not represent genetic re- 

 lationship so well as a classification adopted by Senn (Engler 

 and Prantl, Pflanzenfamilien) based upon the type of meta- 

 bolism. But the older classification, based upon the flagella, 

 is more convenient to use and is of more practical value in the 

 identification of types. For this reason it has been adopted in 

 this preliminary report. 



Key to Orders. 



With one or more flagella, without a collar, and without 



a transverse furrow FLAGELLATA, p. 19 



With one flagellum whose base is surrounded by a collar. , 



CHOANOFLAGELLATA, p. 38 



With two flagella, one of which lies in a cross furrow, and 

 the other in a longitudinal furrow directed backwards. 

 Sometimes naked and colorless; sometimes with a 

 tabulated armor, colored green, yellow, or brown by 

 chromatophores DINOFLAGELLATA, p. 39 



ORDER FLAGELLATA. 



i 



Key to Sub-Orders. 



1. One flagellum, or several flagella, mostly directed 



forward 2 



Usually two flagella of different sizes, one of which 

 is directed forwards and the other backwards. . . . 



HETEROMASTIGODA, p. 29 



2. Mostly small, with one large flagellum and frequently 



one or more smaller secondary flagella 



MONADINA, p. 20 



