floating or sedentary attached unicells of various forms, crescent- 

 shaped, quadrangular, or pyramidal, with the angles extended into 

 horns or spines. Usually the wall is thick and shows lamellations 

 where it is thickened at the poles or angles. Many have an expression 

 similar to the encysted phase of the motile Peridiniales. In theii" 

 reproductive methods the Dinococcales employ autospores or zoo- 

 spores. There are 2-8 of these formed in a cell. In some forms the 

 zoospores show a transverse furrow and other Gymnodinium fea- 

 tures. The spores, upon escape, enlarge and assume the expression 

 of the nonmotile parent cell. One family is recognized. 



FAMILY DINOCOCCACEAE 



Characteristics as described for the order. 



Key to the Genera 



1. Cells free-floating, lunate or arcuate Cystodinium 



1. Cells attached, transversely ellipsoid or inversely 



triangular in front view 2 



2. Cells triangular or tetrahedral ( especially when 



seen from above ) - Tetradinium 



2. Cells ellipsoid Raciborskia 



CYSTODINIUM Klebs 1912, pp. 384, 442 

 Cells free-floating, lunate or arcuate, the poles extended to form 

 sharp, usually recurved spines; longitudinal and transverse furrows 

 lacking, although the position of the furrows is represented in the 

 swarmers formed by the division of the protoplast within the parent 

 cell; chromatophores several to many, brown, more or less pointed 

 or fusiform discs; nucleus conspicuous and centrally located, pig- 

 ment-spot usually lacking. 



Key to the Species 



1. Cells broadly crescent-shaped, the outer margin broadly convex, 



the inner slightly tumid or straight - C. iners 



1. Cells narrowly crescent-shaped, the outer margin convex, the 



inner margin concave ( sometimes straight in the midregion ) 2 



2. Each pole of the cell ending in a curs'ed spine which is twisted 

 away from the longitudinal axis of the 



cell; cells 65-1 10^ long - - - -- C. Steinii 



2. Each pole of the cells ending in a spine, 1 straight, the other 

 twisted away from the longitudinal axis of 

 the cell; cells 40-60/^ long -- -- C. cornifax 



Cystodinium cornifax ( Schill. ) Klebs 1912, pp. 384, 442 



PI. 91, Figs. 5, 6 

 Cells lunate, the dorsal margin strongly convex, the inner margin 

 concave (shghtly straight in the midregion); poles extended into 



[438] 



