Chalk and Flint of the South-east of England. 75 
species and genera detected in the chalk from various parts 
of Europe, Asia, and America*. It will suffice for my present 
purpose to enumerate a few of these fossil organisms, premising 
that the term Polythalamia, or polythalamian animalcules, de- 
signates the calcareous-shelled foraminifera, as for example, Ro- 
talia, Textilaria, Nodosaria, &e., and that of Infusoria, the sili- 
eeous-shelled animalcules, as Xanthidia, Coscinodisci, &c. ; while 
the name Animalculites, is 2 convenient general designation for 
the fossil remains of both divisions of these microscopic forms of 
animal organization. 
Infusoria of the Chalk—M. Ehrenberg describes one species 
of Eunotia and two of Fragillaria from Gravesend ; and from the 
chalk marls of Sicily several species of Actinocyclus, Coscinodiscus, 
and Gaillonella, which are also found alive in the sea at Cuxhaven. 
The most remarkable forms are certain species of Dictyocha, a 
genus formerly supposed to be extinct, which abound im the 
white marls of the chalk of Cattanisetta, and have lately been 
found living in the Baltic 7. 
Another interesting animaleulite is the Peridinium pyrophorum, 
which occurs in the flint of Delitzsch, and has recently been de- 
tected living and luminous in the Baltic. 
Numerous species of all the above genera abound also in the 
tertiary strata, and were formerly supposed to be absent in the 
secondary formations ; and with the exception of a few kinds to 
be noticed hereafter, my own researches and those of several 
competent observers have not revealed any traces of these orga- 
nisms in the English chalk; we have never found Eunotie or 
Fragillarig in that of Gravesend. Of the microscopic calcareous- 
shelled animalcules, the chalk contains species, said by Ehrenberg 
to be identical with living, of the genera Globigerina, Rosalina, 
Cristatella, Textilaria, Rotalia and Nodosaria ; and so far as my 
observations extend, species of these genera form the greater part 
of the cretaceous animalculites of England. But although it is 
easy to demonstrate the abundant occurrence of these forms in 
some masses of chalk, yet in many of the strata it is scarcely pos- 
sible to detect any well-defined specimens ; and I confess, that 
frequent disappointment in my search for these bodies, had made 
me somewhat sceptical of receiving at their full value, the glow- 
* See a translation of this memoir, with plates, in Taylor’s ‘ Scientific 
Memoirs,’ vol. iii. Art. 13. Also a masterly abstract of Ehrenberg’s ob- 
servations ‘On the Composition of Chalk Rocks and Marls by invisible or- 
ganic bodies,” by Mr. Weaver in the ‘ Annals of Nat. Hist.’ for June and 
July 1841. 
t+ The Dictyoche are polygastric animaleules of the family Bacillaria, 
which are invariably coloured by green granules, and have a slow creeping 
motion. 
G2 
