OF THE FAMILY BACILLARIA. 161 



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 probability 

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

 for in any of the specimens of fresh-water infusorial deposits. 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 indestructible 

 shells are therefore to be found in gi-eater 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 entu-ely 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 mis- 

 taken for magnesia, and Dr. Jackson states that it has actually 

 been sold as such to apothecaries, who were much surprised 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, namely : West 

 Point, from which specimens have been examined by Ehrenberg, 

 whose list of the species is given in Silliman's Journal, volume 

 xxxix, p. 193 ; Blue Hill Pond, and various other localities in 

 Maine, discovered by Dr. Jackson ; Manchester, Spencer, Wren- 

 tham, Bridgewater, Andover, &c., in Massachusetts, discovered 

 by Prof. Hitchcock ; and Smithfield and other places in Rhode 

 Island, discovered by Owen Mason, Esq. The lai-gest and most 

 conspicuous species from all these localities are Navicula viridis, 



PI. II, fig. 16, Navicula ? PI. II, fig. 23, Cocconema , 



PI. Ill, fig. 11, Eunotia arcus, PL II, fig. 26. With these occur 

 various smaller species, and numerous siliceous spiculee of fresh- 

 water sponge, PI. Ill, fig. 18, a to d^ and other siliceous bodies of 



