precingular, the 2 antapical and 2 postcingular plates. This means 

 that the plane of division and separation of plates is oblique. The 

 daughter protoplasts continue to move about and gradually build 

 in the necessary complement of plates. 



CERATIUM Schrankl793, p. 34 



In this genus there are broadly fusiform cells which have 3 or 4 

 horns, one anterior and 2 or 3 posterior. The epivalve of the theca 

 (broad just above the girdle) soon narrows abruptly to form the 

 apical horn, which is composed of 4 plates. The hypotheca has 5 

 postcingular and 2 antapical plates, the latter forming the longest 

 posterior horn. In forms which have 3 posterior horns, one is very 

 short. There are no broad sutures between the plates as in some of 

 the related genera. The transverse furrow opens into a broad longi- 

 tudinal sulcus. The entire theca is uniformly marked with a fine 

 reticulum, the meshes of which are 5- or 6-sided. There are numer- 

 ous brown disc-like chromatophores which are often obscured by 

 the semi-opaqueness of the theca. 



Most species of Ceratium are marine but there are a few fresh- 

 water plankters, usually occurring more abundantly in hard water 

 than in soft water lakes. 



Key to the Species 



1. Apical horn long and tapering, as long as or longer than the 



cell body and the posterior horns C. hirundinella 



1. Apical horn shorter than the remainder of the cell 2 



2. Apical horn sharply curved and tapering 



to a blunt point C. carolinianum 



2. Apical horn straight but directed at an angle from the longitudinal 



axis; squarely truncate at the apex C. cornutum 



Ceratium carolinianum (Bailey) Jorgensen 1911, p. 14 



[C. curvirostre Huitfeldt-Kaas] 



PI. 92, Figs. 2, 3 



Cells broadly fusiform in outline; epivalve broad above the 

 transverse furrow, narrowed abruptly to form a stout, curved apical 

 horn, with a shoulder on each side at the base; transverse furrow 

 relatively narrow; hypotheca broad, with a short diverging horn 

 on the left (as seen from the ventral surface), and a longer central 

 horn which is somewhat obliquely directed; cells 65-80/i, in diam- 

 eter, about twice as long as broad. 



Plankter; in Sphagnum bogs, ponds and ditches. Wis. 



[436] 



