No. 2.] FRESH-WATER PROTOZOA. 39 



ORDER DINOFLAGELLATA. 



Key to Genera. 



1. Without membrane surrounding the body 2 



With membrane surrounding the body 3 



2. Cross furrow extending only around left side 



Hemidiniiim 



Cross furrow extending wholly around body 



Gy mno dinium* 



3. Membrane delicate, structureless, no processes .... 



Gleno dinium* 

 Membrane of polygonal plates ; processes, where 



present, small Peridinium* 



Membrane of plates with long horn-like processes 



Ceratium 



Membrane showing a cross furrow near anterior end, 



but no processes Amphidinium 



The genera Gymnodinium, Glenodinium, and Peridinium 

 "have been found abundantly, but I have, as yet, made no fig- 

 ures of them, and their description is, therefore, reserved for 

 a later publication. 



CLASS CILIATA. 

 Key to Orders. 



1. Mouth in a spiral zone of large cilia 3 



2. Mouth without a definite spiral zone 



HOLOTRICHA, p. 39 



3. Adoral zone wound to the left; body also uniformly 



ciliate HETEROTRICHA, p. 53 



Adoral zone wound to the left ; ventral surfaces with 

 characteristically arranged large cilia, while the 



dorsal surface carries only fine cilia or none 



HYPOTRICHA, p. 56 

 Adoral zone wound to the right, usually forming an 

 almost complete circle PERITRICHA, p. 62 



ORDER HOLOTRICHA. 

 Key to Genera. 



I. Solitary 2 



Colonial Maryna 



