450 FORAMINIFERA, POLYCYSTINA, AND SPONGES. 



of Messina, only the upper part or vault of the shell, and to be 

 very regularly divided into four lobes. It is a peculiar feature 



in these Polycystinse, that 

 Fig. 210. Fio. 211. their shells are often pro- 



longed into spines or other 

 projections, which are some- 

 times arranged in such a 

 manner as to give them a 

 very singular aspect (Figs. 

 210, 211). It seems pro- 

 bable that these creatures 

 are almost as widely diffused 

 at the present time as are 

 the Foraminifera ; although, 

 from their greater minute- 

 ness, they have not been 

 so often recognized. For 

 having been first discovered 

 by Prof Ehrenberg at Cux- 

 haven on the North Sea, 

 they were afterwards found 

 by him in collections made 

 in the Antarctic Seas, and have been recently described by Prof. 

 Bailey as presenting themselves (with Foraminifera and Diato- 

 macese) in the deposits brought up by the sounding-lead from the 

 bottom of the Atlantic Ocean, at depths of from 1000 to 2000 

 fathoms. They appear to have been much more abundant, how- 

 ever, during the later geological periods ; for not only have 

 certain forms (among them Haliomma, Fig. 212) been detected by 



Fig 



210. PodocyHis Schoniburgldi. 



211. RhopaUcanimn arnatum. 



FlO. 212. 



Fro. 213. 







Fig. 212. ILilicmma JIumbold/ii. 

 Fig. 213. P^Hchlamydium prcetextum. 



Prof Ehrenberg in the chalks and marls of Sicily and Greece, 

 and of Oran in Africa, and also in the diatomaceous deposits of 

 Bermuda and Eichmond (Virginia) ; but a large proportion of 

 the rock that prevails through an extensive district in the island 

 of Barbadoes, has been found by him to be composed of Poly- 



