[Illustration: FIG. 25. (From Murray and Blackman). _A_, Coccosphere × 1300. _B_, Rhabdosphere × 900. _C_, Portion of the same × 1300. _D_, Rhabdosphere of another type, in optical section × 1900. _E_, The same in surface view × 1900. _F_, End of one of the trumpet-shaped appendages of _E_.] The most recent account of these two genera is by Messrs G. Murray and Blackman a short notice in _Nature_ for April 1, 1897[172]. Numerous examples of Coccospheres and Rhabdospheres were obtained by Capt. Milner of the R.M.S. Para during a voyage to Barbados by allowing the sea water to enter the feed-pipe of the boiler through a fine muslin net. All the forms described in the Challenger Reports were met with, and an examination of the material by means of extremely high objectives has confirmed the original account of the genera, and added some points to our previous knowledge. _Coccospheres_ (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, _C_) 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 Coccospheres 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[173] 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 palaeobotanical 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[174]. Rothpletz[175] has recently recorded the occurrence of numerous Coccoliths, 5–12 µ in diameter, associated with the skeleton of a horny sponge (_Phymatoderma_) of Liassic age.