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 Pohjthalamia, or polythalamian animalcules, de- 

 signates the calcareous-shelled foraminifera, as for example, Ro- 

 t alia J Textilaria, Nodosaria, &c., and that of Infusoria, the sili- 

 ceous-shelled animalcules, as Xanthidia, Coscinodisci, &c. ; while 

 the name Animalculites, is a 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 

 ehalk marls of Sicily several species of Actinocyclus, Coscino discus, 

 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 in the 

 white marls of the chalk of Cattanisetta, and have lately been 

 found living in the Baltic f. 



Another interesting animalculite 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 Eunotia or 

 Fragillaria 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 Glohigetnna, 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. Alsq 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 DictyochcB are polygastric animalcules of the family Bacillaria, 

 which are invariably coloured by green granules, and have a slow creeping 

 motion. 



G2 



