KOPOID AND SWEZY: UNARMORED DINOFLAGELLATA 127 



whieli is strongly compressed laterally (fig. U, 10, 26). This is a condition rare 

 in Gijmnodiuiioii, l)eing met with there mainly in a few fresh- water forms. 

 Correlated with this form of body is the presence of definite chromatophores. 

 These are lacking in one species only, A. scissum, in which the green color is 

 diifiised through the cytoplasm. The chromatophores show three distinct types, 

 which may possibly be only phases related to different stages of metabolism or 

 of the life history. The most common form of chromatophore is that found in 

 A. corpulentum, A. dentatum, A. ovoideum, and A. tnmcatum (figs. U, 6, 4, 19, 

 3). These structures are disklike bodies located in the peripheral layer of the 

 cji;oplasm, and more or less irregular in shape. They are green in A. dentatum 

 and A. truncation, yeWow ochre in A. corpulentum, and bro^^^lish in A. ovoideum. 

 Another phase of these extremely labile organelles may be seen in the smaller 

 green bodies in the peripheral zone of .4. scissum, which may be the remains of 

 larger green chromatophores from which the color has become diffused through 

 the\-ytoplasm (pi. 2, fig. 22). 



Another example of the same type is found in the subgenus Rotundinium 

 in A. pnci^cum (pi. 2, fig. 13), in wdiieh the chromatophores are pyiite yellow. 



The second t^-j^e of chromatophores is shown in A. operculatum, with its 

 long, bandlike chromatophores radiating from a common center near the middle 

 of the body (fig. U, 25). These are also found in A. herdmani and .4. steini 

 (figs. IJ, 2, 28). A slightly different arrangement obtains in A. ktehsi, -where 

 the chromatophores radiate from a conunon center located at the posterior end 

 of the body (fig. U, 14). These are brownish (yellow ochre?) in .4. herdmani, 

 A. steini, and .4. klehsi (?). 



The third t^'j^e of chromatophore is found in the suligenus Rotundi)iiu)n in 

 A. asijmmetricum (pi. 1, fig. 1). The single yellow ochre chromatophore is large, 

 filling almost the entire body, with ramifying, pseudopodia-like projections. 



In the subgenus Fotundinium the body has a robust habit, circular or nearly 

 so in cross-section. With this is correlated, in the larger species, an increasing 

 complexity of cytoplasmic structure, culminating in A. cucurhita (pi. 1, fig. 9). 

 This species resembles, in the structural details of its cytoplasm, the subgenus 

 Pachydinium in Gymnodinium (pi. 3). With four exceptions this group shows 

 a relative absence of chromatophores, the exceptions being A. rotundatum (fig. 

 U, 22). with its peri]iheral, leaf like yelloAV chromatophores, A. asyninirtricum 

 (fig. U, 5), with single, large, yellow ochre chromatophore, A. lacustre (fig. 

 IT, 15), with peripheral, circular, bro-wn chromatophores, A. galhanum (fig. U, 

 29), wdth peripheral, leaf like chromatophores, and A. pacificum (fig. U, 24), 

 with pyrite yellow chromatophores near the surface. 



Tn A. cucurhita, A. cucurhitella, A. fastigium, and ^4. vasculum the color is 

 diffused throughout the cytoplasm, while .4. turbo, A. longum, and A. crassum 

 are colorless. 



The sulcus exhil)its various degrees of development in Ampliidinium. In 

 A. iurho (fig. U, 16) it is a very short, V-shapod indentation of the anterior 



