270 FRESH-WATER BIOLOGY 



208 (207) Cross furrow extending entirely around the body; often flattened. 



Gymnodinium Stein. 

 Representative species. . Gymnodinium fuscum FAircnherg 1838. 



Body oval, compressed, pointed anterioriy. Color light brown. An 

 eye-spot reported by Perty. Length 60 to 80 n. Fresh water. 



^^C^ Fig. 454. Gymnodinium fuscum. X 325. (After Blochmann.) 



209 (206) With a membrane around the body 210 



210(211) Membrane delicate, homogeneous; body without processes, often 



flattened Glenodinium Ehrenberg. 



Representative species. 



Glenodinium pidvisculus Ehrenberg 1838. 



Fig. 455. Glenodinium pulvisculus. X 500 (After Stein.) 



211 (210) Membrane of distinct plates 212 



212 (213) Plates without horn-Hke processes, polygonal, 21 in number. 



Peridiniiim Ehrenberg. 

 Representative species. 



Peridiniiim tahulatmn Ehrenberg 1838. 



Body ovate, with convex dorsal and concave ventral surface. Plates 

 showing a delicate reticulate structure under high magnification. Color 

 yellow, green, or brown. Length 45 to 60 m- Fresh water. 



Fig. 456. Peridinium tabulatum. X 320. (After Stein.) 



213(212) Plates with long, horn-like processes Ceratium ^chx^nk. 



Representative species. . . . Ceratium hirundiftella MuIIgt ij^G. 



Body somewhat quadrilateral, the anterior segment 

 bearing two nearly straight processes and the posterior 

 segment a single short one. Color brown or green. 

 Length go to 170 ij. Freshwater. 



Fig. 457. Ceratium hirundinella. X 325. (After Stein.) 



