158 SKETCH OF THE INFUSORIA 



resulting from increase by spontaneous longitudinal division, 

 resembling chains, little ba7iners, jjlates or ribands. 



Achnanf/ics brcvipcs. (PI. Ill, fig. 12.) Corpuscles striate, curved 

 in tlie middle, ends rounded on the dorsal and ventral sides ; pedicel 

 tliick, shorter than the body. 



I first noticed this species on filaments of Conferva fracta from 

 Providence Cove, R. I., and liave since found it abundant on 

 marine Algae from Stonington, Conn. Small specimens, differing 

 I believe in no essential character, are also very abundant on 

 aquatic plants in the Hudson River at West Point. 



The Achnanthes longipes of authors may be a distinct species, 

 but the distinction " pedicel longer than the body," appears to me 

 to be founded on a character liable to much variation. I saw 

 specimens at Stonington having pedicels much longer than the 

 body, yet they appeared to me to agree mth E. brevipes in every 

 other respect. 



STRIATELLA. 



Carapace simple, ( siliceous, ) fixed by one end, longer than 

 broad, or nearly square, obliquely pedicellate in form of little 

 flags, corpuscles without openings in the middle, often forming 

 zigzag chains by spontaneous divisions. {Stipitate Bacillaricc.) 



1. Striatdla arcuata. (PI. Ill, fig. 13.) Carapace lamellar, nearly 

 square, with three to seven longitudinal internal Hnes, transversely 

 striate, polypidoms (flags) in form of ribands, often curved, nine stria? 

 in one one-hundredth of a line. Diatoma %(nipunctatum, Agardh, 

 Greville, &c. 



This species occurs in vast quantities on filiform marine Algre 

 at Stonington, Conn. It covers the plants in such profusion as 

 to make them gliltor in the sunbeams as if covered with crystals. 

 The recent frustules are not Hat, but slightly convex, and are 

 usually marked with an internal nearly cu'cular spot, which in 

 my specimens was yeUow, not rose-colored as usually described. 

 Considerable variation in the width of the frustules occurs even 

 in the same riband. Each ])late is transversely striate, the alter- 

 nate lines not quite reaching 1o the edge. I saw numerous 

 specimens supported by long pedicels. 



