326 Sketch of the Infusoria of the family Bacillaria. 



Striatella. 



Carapace simple, {siliceovs,) fixed by one end, longer than 

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

 flags, corpuscles without openings in the middle, often forming 

 zigzag chains by spontaneous divisions. {Stipitate Bacillarice.) 



1. Striatella arcuata. (PI. 3, fig. 13.) Carapace lamellar, nearly- 

 square, with three to seven longitudinal internal lines, transversely stri- 

 ate, polypidoms (flags) in form of ribbons, often curved, nine striae in 

 y^^ line. Diatoma unipunctatum, Agardh, Greville, &c. 



This species occurs in vast quantities on filiform marine Alga? 

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

 make them glitter in the sunbeams as if covered with crystals. 

 The recent frnstules are not flat, but slightly convex, and are 

 usually marked with an internal nearly circular spot, which in 

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

 Considerable variation in the width of the frustules occurs even 

 in the same ribbon. Each plate is transversely striate, the alter- 

 nate lines not quite reaching to the edge. I saw numerous spe- 

 cimens supported by long pedicels. 



Sect. IV. LACERNATA. 



Frustulia, Ehr. 



Envelope double, carapace siliceous, mantle gelatinous, amor- 

 phous, corpuscles scattered or in groups. 



I have seen no American species of this genus.* 



Syncyclia. 



Envelope double, exterior mantle gelatinous, carapace sili- 

 ceous, navicula-shaped, forming by spotitaneous division, circular 

 groups surrounded by gelatine. See Pritchard's Infusoria, Plate 

 4, p. 206. 



No American species has yet been detected. 



Naunema, 



Envelope double, carapace navicula-shaped, siliceous ; mantle 

 gelatinous, exterior, tubular ; tubes filiform, separate, branching, 



* My opportunity to study the marine Bacillaria, has been very slight. I pre- 

 sume therefore, that many marine forms not noticed by me during the two days 

 which I spent at Stonington will yet be detected, and among them will probably 

 be species of Frustulia, Syncyclia and Schizonema. 



