OF THE FAMILY BACILLARIA. ' 137 



unable to perceive the " sillon perce " alluded to by Ehrenberg in 

 his specific character. This species might easily be mistaken for 

 a Conferva. It often forms bluish green masses, of full a foot in 

 extent, and while fresh it is quite as flexible as any Conferva ; 

 but on drying, it becomes of a light brassy yellow color, and is 

 then excessively fragile. There is much variation in the diame- 

 ter of the filaments, and in the relative length of the joints. The 

 filaments which have the smallest diameter, have, generally, the 

 longest joints. They retain their forms when heated to white- 

 ness, and when treated with strong nitric acid. This species 

 occurs in springs, rivulets, &c., and appears as common in this 

 country as in Europe. In (PI. II, fig. 4, b,) is represented a spe- 

 cies of Gaillonella apparently distinct from figs. 4 and 4 a. It 

 shows the pierced furrows, and agrees in most respects with the 

 figure of G. aurichalcea given by Ehrenberg in his memoir 

 entitled Die Fossilen Infiisorien und die lehendige Dammerde, 

 PI. 1, fig. 23. It is, possibly, only a state of our species above 

 referred to. It occurs in ponds near West Point. 



3. Gaillonella distans. (Pi. II, fig. 5.) Corpuscles cylindrical, 

 short, truncate and flattened on the ends, smooth, with two pierced 

 furrows, always separated in the middle, -^J-^ to yV of a line, usually 



] 



This species occurs in vast quantities in the fossil state in 

 Europe. It constitutes a large portion of the slate of Bilin and 

 Cassel, and of the " Berghmehl " or " fossil farina " of various 

 localities. It occurs in most of the specimens of American fossil 

 infusoria, which I have seen. It is particularly abundant in the 

 specimens from Manchester, Mass., which are chiefly composed 

 of exceedingly minute frustules of this species. It forms here, 

 a true fossil farina, almost as light as flour, and containing in a 

 cubic inch many hundred millions of these minute siliceous shells. 

 It occm's in a living state at West Point. 



4. Gaillonella varians. (PI. II, fig. 6, a, b.) Corpuscles flat on 

 each end, cylindrical surface smooth, ends with fine radiating lines, 

 ovaries yellow or green, -j-^^- to one fortieth of a line. 



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