120 On the Microscopical Siliceous Polycystina of Barbados, 



The fossil species have been found partly in the calcareous 

 marls (Kreidemergel) from Sicily, partly in the Tripoli forma- 

 tion of Oran, Engia, Zante, from different localities in Virginia 

 and the Bermuda Isles. These different localities belong, ac- 

 cording to the prevailing opinion of geologists, to two different 

 periods ; and it is consequently important to separate the differ- 

 ent species of Polycystina which have been found in them. 



In the monthly report of the Royal Academy, Ehrenberg de- 

 scribed in 1844 eighteen species of Polycystina which had been 

 found in the chalk-marls of Caltanisetta. The remainder, with 

 the exception of the five recent forms, would belong to the ter- 

 tiary formation. 



In possession of the materials above indicated, to which may 

 be added a few recent observations that increase the number of 

 fossil species of the tertiary period, Professor Ehrenberg now 

 compares the numerous forms which he found in the rocks from 

 Barbados, 1st, with the recent forms; 2ndly, with those of 

 the tertiary rocks; and 3rdly, with the forms from the chalk 

 or secondary period. The result of the comparison is — that of 

 the 282 species minus 15 which form the rocks in Barbados, only 

 one species (namely Haliomma ovatum) can be said with certainty 

 to occur among recent species. Of the eighteen species formerly 

 described as belonging to the chalk formation are eight among 

 the 282 fossil species from Barbados, and a new revision of the 

 Sicilian marls rewarded Professor Ehrenberg with the discovery 

 of six additional species ; consequently altogether fourteen which 

 do not differ from those in Barbados specifically, but may be 

 perhaps slight varieties. They are — 



Cornutella clathrata. Haliomma Medusa. 

 Lithobotrys acuta. nobile. 



Lophophaena obtusa. Entactinia. 



Eucyrtidium Eruca. Dictyospyris tristoma. 



lineatum ? Ceratospyris radicata. 



Cycladophora spatiosa. FJustrella conccntrica. 



Haliomma Dixiphos. Astromma Entomocora? 



Ten of the forms discovered on a former occasion in the 

 chalks of Sicily were not observable in the rocks from Barbados, 

 and one species, Eucyrtidium lineatum, which is most abundant 

 in Sicily, and which occurs likewise in the so-called tertiary 

 rocks, is not only very scarce in Barbados, but its identity is like- 

 wise doubtful; however, forms nearly related to it are so very 

 numerous in Barbados that they compose whole masses of rocks. 

 The so-called tertiary Tripoli and tertiary marl, or halibiolithic 

 rocks, from Oran, Engia, Zante, Virginia, Bermuda, contain only 

 a few Polycystina interspersed here and there : their masses are 

 formed of poly gastric shells. According to the former commu- 

 nications of Professor Ehrenberg, they contained twenty-one 



