328 Sketch of the Infusoria of the family Bacillaria. 



Mr. Berkely has recently published (Ann. and Mag. Nat. Hist. 

 Vol. 7, p. 449) some interesting observations, by which he ap- 

 pears to have proved that the only species of this genus, the sin- 

 gular G. paradoxum, consists merely of rows of ova of some 

 aquatic insect. He watched their development into larvae. I 

 have not seen American specimens. 



SCHIZONEMA. 



Envelope double, carapace siliceous, mantle tubular, tubes uni- 

 ted in bundles, split in some places so as to appear branched, cor- 

 puscles like those of Navicula. 



No American species has yet been detected by me. 



End of the Bacillaria. 



It was my intention when I commenced the above sketch, to 

 give in connection with it, an account of all the American local- 

 ities of fossil infusoria, but further reflection has convinced me 

 that this labor is unnecessary. All our fluviatile deposits of fossil 

 infusoria, contain nearly the same species, and all these species 

 are now living. From the great range which the living species 

 have been shown to have in our country, there is great probabil- 

 ity that all of the siliceous ones may be detected, if carefully 

 sought for -in any of the specimens of fresh-water infusorial de- 

 posits. As for the localities at which these fossil infusoria occur, 

 it does not appear that a particular enumeration is necessary. 

 The living animals inhabit in great quantities almost every place 

 where water remains several months in the year, their indestructi- 

 ble shells are therefore to be found in greater or less quantity in 

 the sedimentary deposits of all our bogs, ponds and slow streams. 

 These deposits are most remarkable beneath peat bogs, where 

 they constitute strata many feet in thickness, and of great extent, 

 often composed entirely of the siliceous carapaces of animals 

 so minute that millions of them exist in a cubic inch. The 

 "siliceous marl" which they form, is often so white and light as 

 to be mistaken for magnesia, and Dr. Jackson states that it has 

 actually been sold as such to apothecaries, who were much sur- 

 prised when informed by him that not a particle of magnesia 

 was present. 



Among the vast number of fluviatile localities now known, I 

 think it necessary to allude only to the following, viz. West 

 Point, from which specimens have been examined by Ehrenberg, 



