120 THALLOPHYTA. [CH 



objectives has confirmed the original account of the genera, 

 and added some points to our previous knowledge. 



Goccospheres (fig. 25 A). Spherical bodies of exceedingly small 

 size, consisting of a central protoplasmic vesicle covered with 

 overlapping circular calcareous scales, each of which is attached 

 to the minute cell by a button-like projection. The scales 

 are frequently found detached and are then spoken of as 

 Coccoliths. 



Rhabdospheres (fig. 25 B — F). Spherical bodies, extremely 

 minute, consisting of a single cell, on the surface of which are 

 embedded numerous calcareous plates bearing long blunt spines 

 (fig. 25, 0) or beautiful trumpet-like appendages (fig. 25, D — F). 

 The detached plates of Rhabdospheres are known as Rhabdoliths. 



In addition to the text-figures of Goccospheres and 

 Rhabdospheres in the Challenger Reports, the same structures 

 are shown in samples of globigerine ooze figured in Plate XI. 

 of the Monograph on deep-sea deposits. In a recent number of 

 Nature Messrs Dixon and Joly ^ have announced the discovery 

 of Coccoliths and Coccospheres in the coastal waters off South 

 County Dublin. They estimate that in one sample of water 

 taken about three miles from the Irish coast there were 200 

 Coccoliths in each cubic centimetre of sea water. 



The interest of these calcareous bodies from a palaeobotani- 

 cal point of view lies in the fact that similar forms have been 

 recognized in the Chalk and the Upper Lias. Sorby, in his 

 memorable Address delivered before the Geological Society in 

 1879, refers to the abundance of Coccoliths in sections of chalk 

 which he examined^ Rothpletz^ has recently recorded the 

 occurrence of numerous Coccoliths, 5 — 12 fju in diameter, associ- 

 ated with the skeleton of a horny sponge (Phymatoderma) of 

 Liassic age. 



The question of the nature of Coccospheres and Rhab- 

 dospheres cannot be regarded as definitely settled. It has 

 been shown by J. Murray, and more recently by G. Murray 

 and V. H. Blackman, that on the solution of the calcareous 

 material by a weak acid there remains a small gelatinous body 



1 Dixon and Joly (97). ^ go^by (79) p. 78. 



> 3 Kothpletz (96), p. 909, PI. xxiii. fig. 4. 



