118 THALLOPHYTA. [CH. 



of the recent species Peridinium divergens Ehrenb., as given by 

 Schiitt' and other writers, brings out clearly the very close 

 resemblance if not identity of the two forms. Butschli^ in 

 his account of the Dinoflagellata in Bronn's Thier-Reich 

 confirms Ehrenberg's determination of Peridinium pyrophorum, 

 and points out its striking agi-eement with the recent species. 



II. COCCOSPHERES AND RHABDO SPHERES. 



(Organisms of doubtful affinity.) 



Our knowledge of these minute calcareous organisms is 

 derived from Huxley's description of coccoliths from the 

 Atlantic in 1857, and from the accounts of Wallich, John 

 Murray, and other writers. In the first volume of the narrative 

 of the Challenger cruise' and in the volume on deep-sea 

 deposits* these minute forms of life are figured and described. 

 In the latter volume both genera are spoken of as extremely 

 abundant in the surface waters of the tropical and temperate re- 

 gions of the open ocean, and as forming an important constituent 

 of the Globigerine ooze ; they are said to occur entangled in the 

 gelatinous substance of the Radiolarians, Diatoms, and Forami- 

 nifera, and are very common in the stomachs of Salps, Pteropods 

 and other pelagic animals. Rhabdospheres are rare in regions 

 where the temperature of the water sinks below 6.5° F. ; the 

 Coccospheres occur in tropical and temperate latitudes, and 

 extend further north and south than the Rhabdospheres. As 

 regards their botanical position, John Murray expresses the 

 view that they are in all probability pelagic algae. 



In the interesting memoir by Schutt on the Pflanzenlehen 

 der Hochsee^ there occurs a short reference to the forms de- 

 scribed in the Challenger Reports, but they were not obtained 

 by the staff of the Hensen Plankton Expedition and Schutt's 

 remarks are not based therefore on personal observations. 

 While admitting the existence of such bodies, he points out 

 that Zoologists have referred Coccospheres and Rhabdospheres 



1 Schiitt (96) p. 22. 2 Butschli (83-87) p. 1028. 



3 Challenger Reports (85) p. 939. ■• Challenger Reports (91) p. 257. 



s Hensen (92), Sohutt (93) p. U. 



