FOEAMINIFERA. 



1)5 



Fig. 24. Fabularia discolithes (Pefrance). 

 Natural fcize and magnified. 



rapidly in the Tertiary period, where they attain the maximum of 

 their numerical development. In the celebrated quarries of St. Peter, 

 at Maestrecht, the Siderolites 

 calcitrapoides of Lamarck are 

 found in the upper chalk (Fig. 

 23). In the calcareous forma- 

 tion of Chaussy, in the Seine 

 and Oise district, and other 

 parts of the Paris basin, the 

 Fabularia discolitlies (Fig. 24) 

 of Defrance is found. Finally, 

 the Dactylopora cylindracea of 

 Lamarck (Fig. 26) is found in 

 the eocene formation of Val- 

 mondois and in the chalk of 

 Grignon. At first, this little 

 creature was thought to be a 

 polype ; but d'Orbigny, in his 

 " Prodrome de Paleontologie," 

 has placed it among the Fora- 

 minifera, thinking that it ap- 

 peared to occupy a place be- 

 tween the two classes. 



The existing Foraminifera 



Hg 25. Alveolina oblonga (d'Orllgny). 

 Natural size and magnified. 



are by no means equally dis- 

 tributed in every ocean. Some 

 genera belong to warm coun- 



. . , , , Fig. 26. Dactylopora cylindracea (Lamarck), 



tries, Others tO temperate and Natural size and magnified. 



cold climates. They are much more numerous, however, and much 

 more varied in their forms, in warm than in cold climates, and, we 

 may add, larger also, for Sir E. Belcher brought a recent species 

 from Borneo which measured two inches in diameter. 



Before passing on to the study of the Infusoria, a few words may 

 be offered on the Noctiluca, a genus of animals usually referred to 

 the class ACALEPHJE. One species only of this genus has been 

 described, which occurs occasionally on the English coast in prodigious 

 numbers. It is a small creature, scarcely the hundredth part of an 



