Sketch of the Infusoria of the family Bacillaria. 287 
izes’ 3, Fixed obliquely. ; . 
a aa. Opening in the m iddle, ne aa Achnanthes.* 
iol Without opening in the middle, -  Striatella.* 
B. Carapace povs Lacernata : 
_. A. Surrounded ‘ns an amorphous ecltinow mass. 
a, Scattered, _ abies Ssrnielia, i 
b, Joined in rings, 1 SPCR: Syneyelia. 
B. Surrounded by iudiabtinbas wined — e 
- a. Tubes separate. ; 
a. Frustules strait, 42 ped ee a . ~ Naunema.* 
og 1 eerie aon peere Raa -  Gloenema. 
 @, Fasciculate, Fa. ae Sey rompers 
b. Branching romega. 
The marked a (*) have: ines Spinetaits in the United Sina, 
Ehrenberg remarks of this family, that “the organization is difficult 
to tage in consequence of the hardness and refraction of the ca- 
rapace. . None have yet been found with calcareous coverings, but 
they are either hard and siliceous, (sometimes containing a little iron,) 
or membranaceous without silica. The differences observed in the 
in = hyaline 
vesicles of variable form; these are colorless, and resemble the stom 
achs of the Polygastrica, and in recent expe hens 
less granules, forming two or four groups, ¥ 
middle of the body, as in Navicula, Cocconema, aaeoas ec. Yio 
eggs are frequently divided into several globular groups which finally 
unite in a cruciform manner (Achnanthes) or which become confound- 
ed together, before being emitted, (Gallionella, Pyxidicula, Isthmia, 
&e. ;) at other times they appear under the form of a tube enveloping 
ae stomachs and other organs, (Xanthidium, Euastrum, Fee sige scorn 
genera Micrasterias, Arthrodesmus, Tessararthra and Xanthidium, 
have organs which may be compared to seminal vesicles. Spontane- 
ous division produces much variety in the forms of the polypidoms. 
It sometimes takes place longitudinally, sometimes transversely.” ~ 
~ "The living species of this family may be found in slniatdwuny: 
situation where water occurs upon the surface of the earth. Some _ 
genera are exclusively marine, others are exclusively fluviatile, 
while some genera, as Navicula, Gomphonema, &c., include both 
salt and fresh water species. ‘The marine species may often be 
. found in great quantities among the filiform Algrey-w which hey 
with their apenee: Calay 
syd ‘itn a 
ie oy pt gist P Sy eh bey ‘ 
