OF THE FAMILY BACILLARIA. 149 



COCCONEIS. 



Free, single, carapace simple, bivalve {siliceous) prismatic or 

 hemispherical, a single opening in the middle of both sides of the 

 carapace {?), never double or catenate by spontaneous division. 



1. Cocconeis ? (PL II, fig. 34.) Represents what I believe to be 

 a species of Cocconeis. I found it adhering to a small marine Alga 

 from the eastern shore of Florida. A similar form is abundant in 

 Boston harbor. 



Beautiful figures of Cocconeis {Campylodiscus) clypeus drawn 

 by F. Bauer, will be found in Pritchard's Hist. Inf., PL 12, fig. 

 516-518. I have received fine specimens of these elegant fossils 

 from E. J. Quekett, Esq., of London. 



BACILLARIA. 



Free, [never fixed) carapace simple, bivcdve or muUivalve (sili- 

 ceous) prismatic, forming chains or zigzag polypidoms by imper- 

 fect spontaneous division of the carapace and perfect division of 

 the body. 



1. Bacillaria paradoxa. (PL II, fig. 35.) — TJie standard hearer. 

 Striate, carapace linear, very slender, often fifteen times longer than 

 broad, yellow, frustules very active, -^^ to J^ of a line. Syn. Vibrio 

 paxillifer, Midler. See Encyl. Meth. PL 3, fig. 16 to 20. 



I first detected this species in October, 1840, among Algae from 

 the Hudson River, near West Point. I am informed by Dr. P. B. 

 Goddard, of Philadelphia, that it also occurs in abundance near 

 that city. It is a very interesting species, presenting by its curious 

 motions and paradoxical appearance, an object well calculated to 

 astonish all who behold it. At one moment, the needle-shaped 

 frustules lie side by side, forming a rectangular plate ; suddenly, 

 one of the frustules slides forward a little ways, the next slides a 

 litde also, and so on through the whole number, each however 

 retaining a contact through part of its length with the adjoining 

 ones. By this united motion the parallelogram is changed into 

 a long line ; then some of the frustules slide together again, so 

 that the form is then much like a standard. Similar motions 

 are constantly going on, and with such rapidity that the eye can 

 scarcely foUow them. There are few more interesting objects for 

 the microscope. 



