326 Sketch of the Infusoria of the family Bacillaria. 
STRIATELLA. 
Carapace simple, (siliceous,) fixed by one end, longer than 
broad, or nearly square, obliquely pediculate in form of liitle 
flags, corpuscles without openings in the middle, often forming 
zigzag chains by spontaneous divisions. (Stipitate Bacillarie.) 
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 strie in 
zda line. Diatoma unipunctatum, Agardh, Greville, &c. 
This species occurs in vast quantities on filiform marine Alge 
at Stonington, Conn. It covers the plants in such profusion as to 
make them glitter in the sunbeams as if covered with erystals. 
The recent frustules 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. 
Secr. IV. LACERNATA. 
Frustuuia, Ehr. 
Envelope double, carapace siliceous, mantle gelatinous, amor- 
phous, corpuscles scattered or in groups. 
I have seen no American species of this genus.* 
Syneye.ia, 
Envelope double, exterior manile gelatinous, carapace sili- 
ceous, navicula-shaped, forming by spontaneous division. 
groups surrounded by gelatine. See Pritchard's infontaie; Plate 
A, p. 206. 
No American species has et been detected. 
Navnema. 
Envelope double, carapace navicula-shaped, siliceous ; mantle 
ecetinns, exterior, tubular ; tubes filiform, separate, branching, 
phrase Ae in aco A 
wee not t noticed by me 
and 
ot 
