270 FRESH-WATER BIOLOGY 



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



Gymnodinium Stein. 

 Representative species. . Gymnodinium fuscum Ehrenberg 1838. 



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

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



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 pulvisculus Ehrenberg 1838. 



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



211 (210) Membrane of distinct plates 212 



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



Peridinium Ehrenberg. 

 Representative species. 



Peridinium tabulatum 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 /*. Fresh water. 



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



213(212) Plates with long, horn-like processes Ceratium Schrank. 



Representative species. . . . Ceratium hirundinella Miiller 1786. 



Body somewhat quadrilateral, the anterior segment 

 bearing two nearly straight processes and the posterior 

 segment a single short one. Color brown or green. 

 Length 90 to 170 /i. Fresh water. 



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



