Ceratium cornutum ( Ehrenb. ) Claparede 



& Lachmann 1858, p. 394 



PL 92, Figs. 8,9 



Cells broadly fusiform in outline, stout, the epitheca broad above 

 the transverse furrow, the sides rapidly converging and narrowed 

 to form a short, stout anterior horn which extends obliquely and is 

 truncate at the apex; transverse furrow relatively broad; hypotheca 

 broad below the furrow, extended into 2 horns, 1 short lateral horn 

 and 1 longer and median; cells 75-80/a in diameter, about as long 

 as wide, or slightly longer. 



Rare; in the plankton of soft water lakes. Mich., Wis. 



Ceratium hirundinella (O. F. Muell.) Dujardin 1841, p. 377 



PI. 92, Figs. 4, 5 



Cells broadly or narrowly fusiform in outline, depending upon 

 the degree of divergence of the horns; very much flattened dorsi- 

 ventrally; epitheca with sharply converging margins from just above 

 the transverse furrow, then narrowed more gradually to form a long 

 horn; transverse furrow relatively narrow; body of the hypotheca 

 broad and short below the transverse furrow, divided into a varying 

 number of posterior horns, usually 3, sometimes only 1, the central 

 or median horn the longest and formed by the antapical plates; 

 plates coarsely reticulate; cells varying in size depending upon 

 environmental conditions, 100-400fi long. 



This species is very common, especially in hard water lakes, where 

 occasionally it may become so abundant as to color the lake a deep 

 brown. Such blooms develop and disappear suddenly. 



This species shows a great variation in the form of the cell, num- 

 ber of horns, etc., and it is often the subject of ecological and 

 limnological studies. It shows a remarkable periodicity and may 

 exhibit a vertical distribution which is accompanied by some inter- 

 esting relationships between the length of the horns and buoyancy; 

 form of the cell and temperature, etc. 



The tremendous amount of nitrogen, phosphorus, and products 

 of photosynthesis which accumulate in these organisms when they 

 develop a bloom must certainly produce interesting limnological 

 effects in a lake. In spite of the wealth of literature on this genus, 

 very little seems to have been published on the role that these 

 species play in lake biology. 



Mich., Wis. 



ORDER DINOCOCCALES 



These are forms which are not motile in the vegetative state and 

 which are incapable of cell division. They exist as either free- 



[437] 



