The Mastigophora 129 



characteristic siliceous skeleton varies in complexity in difierent species 

 and has been interpreted as an external structure and as an internal 

 one (Fig. 4. 9, I) by different workers (63). A single flagellum, numerous 

 greenish-brown chromatophores, and stored granules of leucosin appear 

 to be typical. 



Generic boundaries have been disputed to some extent. However, 



^J^ 



Fig. 4. 10. Coccolithina. A. Discosphaera tubifer (Murray and Black- 

 man) Lohmann: schematic optical section showing rhabdoliths and two 

 chromatophores; x2800 (after L.). B. Single rhabdolith from Rhabdo- 

 sphaera claviger M. and B.; schematic (after Murray and Blackman). C. 

 Rhabdosphaera stylifer Lohmann, showing nucleus and two chromato- 

 phores; x2100 (after L.). D. Surface view of placolith from Coccolithus 

 wallichi; x2700 (after Lohmann). E. Optical section of coccolith from Coc- 

 colithus pelagica; schematic (after Murrav and Blackman). F. Coccolithus 

 ivallichi showing arrangement of coccoliths; xl800 (after Lohmann). G. 

 Hymenomonas roseola Stein; xT'jO (after Pascher). H. Longitudinal section 

 of rhabdolith from Discosphaera tubifer; schematic (after Lohmann). L 

 Syracosphaera pulchra. anterior coccoliths with spines; xl900 (after Loh- 

 mann). 



