STILL FOUND IN A LIVING STATE, - 349 
genus Actinocyclus with rays without septa, of which previ- 
ously no living species was known, and which might have been 
regarded as especially characteristic of the chalk formation, but 
which in fact it is not. 
Recent repeated examinations of the chalk marl have con- 
vinced me, then, that two long-known siliceous-shielded ani- 
malcules, Striatella arcuata and Tessella Catena, which are of 
exceedingly frequent occurrence in the water of the North Sea, 
and also abundant in that of Tj6rn, are likewise present in small 
number in those marls ; and also the centrally constricted Navi- 
cula Didymus, which I had first observed near Cuxhaven, was 
detected, on further research, as empty shells in the chalk mar] 
from Caltanisetta. 
I had, moreover, succeeded, up to August 1840, in detecting 
Coscinodiscus lineatus and three calcareous-shelled Polythalamia 
as still living, in the salt water from Cuxhaven, which had been 
preserved and frequently examined, viz. Rotalia globulosa, R. 
perforata, and Textilaria globulosa,—also species of those very 
genera, which, according to my previous memoirs, have essen- 
tially contributed to the formation of the chalk rocks. 
These twenty recently-observed forms, then, added to the 
twenty species previously published in October 1839, increased 
our knowledge of still existing chalk animals to forty species. 
I will now add some observations of the latest date. I have 
_ discovered among the living forms in the salt water from Tjérn 
| Actinocyclus quinarius and Coscinodiscus eccentricus, together 
with Grammatophora angulosa as found at Oran. I have further 
detected, by a repeated examination of the chalk marl from 
Greece forwarded to me by M. Fiedler of Dresden, and espe- 
cially of that numbered 5, which, as stated in his ‘Travels’ 
(i. p. 224), appears in A%gina to form the base and principal 
mass of a trachytic mountain, an unexpectedly great number of 
recent forms, and there associated with decided chalk animals. 
The composition of this Greek marl is perfectly identical in 
many characteristic forms with the chalk marl of Caltanisetta; 
and contains, together with these, others which coincide so per- 
fectly with those from Oran, that even now I must consider 
that geognostical stratum as chalk. On a fresh examination I 
was at once surprised by the characteristic Grammatophora 
undulata of the Mexican sea-coast, and likewise by Dictyocha 
(Actiniscus) Pentasterias, but recently and first observed in the 
sea-water from Christiania. There were also found Triceralium 
