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APPENDIX. 



nella sulcata, may be shewn as the chief forms met with in 

 examining the chalk marls of Sicily, and also that the 

 species of the chalk formations are yet to be found as 

 crowds of living creatures in the waters of our seas. 



(a). Climatorial Helationships. — Europe, Africa, Asia, 

 America, and the Isle of Bourbon, exhibit the same crea- 

 tures, partly in a fossil condition, and partly alive, in 

 various relationships, as has been already shewn, but 

 which knowledge has lately been most materially extended, 

 as also that concerning the general distribution of the 

 same species, both in fresh water and the sea. So general, 

 in fact, is such distribution, that the forms of the Siberian 

 Alps, the Altai Mountains (high lands of upper Asia), and 

 those of the waters near Berlin, and of the Nile, at Don- 

 gola, are so similar, that, to a certain extent, when brought 

 together and compared, no differences, agreeing with the 

 principles of natural history, could be discerned. 



{b.) Self-division. — The importance of this power, so 

 forcibly exhibited in the various tribes of animalcules, is 

 well shewn by the fact that a creature, invisible to the 

 naked eye, can, in the space of four days, give origin 

 to no less than 140 billions of beings; and as, from the 

 size, &c. of the bodies, we can easily calculate that 

 40,000 millions of individuals exist in a cubic inch of the 

 polishing slate of Bilin, so 70 billions must be necessary 

 to form a cubic foot of the same structure. 



Genus Amphitetras belongs to the family Bacillaria, 

 and must be ranged under section Naviculaceae. Its 

 members are characterized by being unattached, and hav- 

 ing a simple bi- or multi-valved siUceous lorica, which is 

 square, and has four openings, situated at the angles of 

 its opposed lateral faces. The self-division is imperfect, 

 but the chain-like masses which the individuals form are 

 not gaping, like some other genera. 



733. Amphitetras antediluviana, — Each shell-like 



