72 WISCONSIN PHYTOPLA.NETON 



Family DINOBRTONACEAE. 



Cells solitary or in colonies, free-floating or sessile. Always attached 

 to the base of a conical to vase-like, colored or hyaline, smooth or sculp>- 

 tured receptacle. Cells with one or two laminate chromatophores, con- 

 tractile vacuoles, an eyespot, and two cilia of unequal length. 



KEY TO THE GENERA. 



Receptacles homogeneous, without growth rings DINOBRYON 



Receptacles with successive growth rings HYALOBBYOX 



DINOBRYON Ehrenberg 1835. 



Cells free-floating, sessile, or epiphytic; solitary or in colonies; at- 

 tached to the bottom of conical, campanulate, or cylindrical receptacles 

 with open apices and pointed bases. Colonial species arbuscular, each 

 receptacle with the pointed ends of 1-4 other receptacles in its mouth. 

 Development of branching indefinite. Protoplast spindle-shaped, coni- 

 cal, or ovoid ; attached by a stalk to the base of the receptacle. Anterior 

 end of protoplast with two cilia of unequal length that project beyond 

 the open end of the receptacle. Cells with one or two laminate, elon- 

 gate, parietal, golden-brown chromatophores; several apical, lateral, or 

 basal contractile vacuoles; and one apical eyespot. Assimilation pro- 

 duct generally leucosin. 



Reproduction by longitudinal division of cell contents to form ovoid 

 daughter cells that migrate to the mouth of the old receptacle or leave 

 it entirely before developing new receptacles. Akinetes known. 



The specific limits of colonial plankton species of this genus are very 

 poorly defined and it is almost impossible to draw a sharp line of de- 

 marcation between the various species. I have indicated as species the 

 centers around which the variations seem to occur. 



KEY TO THE SPECIES. 



Cells solitary. 



Cell shape conical, elongate D. CALICIFORMB 



Cells broadly spindle-shaped D. TABELLABIAE 



Cells in colonies. 



Branching of cells markedly divergent D. DIVKEGEXS 



Branching of cells not sharply divergent. 

 Cells elongate conical. 



'Sides of receptacles straight D. STim-ATUM 



Sides of receptacles undulate D. BAVABICUM 



Cells campanulate , .D. SJTTULABIA 



