No. 2.] FRESH-WATER PROTOZOA. 53 



Ch. vorax Stokes, Fig. i8o. 

 Ch. caudatus Stokes, Figs. i66 and 173. t 

 Ch. megalotrocha Stokes, Fig. 168. An extremely com- 

 mon species in infusions. 

 Ch. sp. (?), Fig. 172. 

 New Genus (?). 



Body nearly spherical in outline, with a slight lip at 

 anterior end, at bottom of which is found a mouth. Six 

 prominent rows of cilia on ventral surface, extending 

 from pole to pole. Nucleus and contractile vacuole pres- 

 ent, posterior. Motions slow. No evident pharynx. 



Fig. 184. This peculiar animal has been found several 

 times in our water. It cannot be placed in any genus 

 known to me. 



ORDER HETEROTRICHA. 

 Key to Genera. 



1. With undulating membrane 2 



Without undulating membrane 3 



2. Flattened ; narrowed in front, peristome long, on left 



Blepharisma* 

 Cylindrical or purse-shaped ; not flattened ; peristome 



short, inclosing the wide anterior end. .Condylostoma* 

 Body more or less spiral ; peristome furrow-shaped . . 



Met opus* 



3. Membranellse evident and somewhat spiral 4 



Membranellse not spiral, feather-like ; body in a 



lorica 5 



4. Long, thread-shaped, or somewhat flattened 



Spirostomum* 

 Purse-shaped; oblique in front, peristome funnel- 

 shaped, sunken in the body Bitrsaria* 



Purse-shaped; peristome flat, inclosing whole ante- 

 rior end of body Climacostomum 



Purse-shaped ; peristome broad in front but not in- 

 closing whole anterior end of the body, extending 

 obliquely to the right Balantidium 



f This is Chilodon caudatus of Stokes, but should perhaps more properly be 

 placed under the generic name Mgyria because of its caudal appendage. JEgyria 

 is said to contain one species only and to be found only in salt water, and that 

 species is certainly not the one described above. 



