FRESH-WATER BIOLOGY 



161 (160) 



Border cilia interrupted at the posterior end. Frontal styles, 

 eight or ten. Five ventral setae and five anal styles. No 

 caudal bristles. Dorsal hispid setae usually present. 



Tachysoma Stokes. 



Representative species. . . . Tachysoma parmstyla Stokes 1887. 

 Body narrow anteriorly forming a neck-like region. Ten 

 frontal styles. Marginal setae scarcely projecting except pos- 

 teriorly. Dorsal setae minute. Styles in this form are very 

 small. Length 60 /*. Shallow pools in early spring. 



FIG. 529. Tachysoma parmstyla. X 450. (After Stokes.) 



162 (159) Body not flexible 163 



163 (164) With caudal setae. Elongate-oval in shape with eight frontal, five 



ventral setae, and five anal styles. Caudal setae usually 

 three, long. Peristome triangular, with an undulating mem- 

 brane; the inner wall bent away from the outer wall. 



Stylonychia Stein. 

 Representative species. , , , Stylonychia notophora Stokes 1885. 



Front border obliquely truncate on the left side. Peristome 

 extending nearly to the middle of the body. Caudal setae 

 widely separated. Nuclei two. Length 120 to 160 p. Pond 

 water. 



FIG. 530. Stylonychia notophora. cv, contractile vacuole; macn, macro- 

 nucleus. X 300. (After Conn.) 



164 (163) Without caudal setae; with inner wall of peristome bent toward the 



outer wall. Like Stylonychia in other respects. 



Histrio Sterki. 

 Representative species Histrio erethisticus Stokes 1887. 



Frontal styles nine; anal styles five, stout, rigid. Mar- 

 ginal setae uninterrupted. Length 1 50 M- Shallow pools, 

 with algae. 



FIG. 531. Histrio erethisticus. X 200. (After Conn.) 



165 (158) Produced posteriorly into a tail-like process. Body flexible, with 



eight ventral setae and five anal styles at the base of the tail. 



Urosoma Kowalewsky. 

 Representative species . Urosoma sp. 



Form doubtful as to species. 

 FIG. 532. Urosoma sp. X 335. (After Conn.) 



166 (131) Border cilia few or none 167 



