Sketch of the Infusoria of the family Badllaria. 287 



3. Fixed obliquely. 



aa. Opening in the middle, . . . Achnanthcs.* 

 bb. Without opening in the middle, . Striatella.* 



B. Carapace double, .... Lacernata. 



A. Surrounded by an amorphous gelatinous mass. 



a. Scattered, ........ Frustulia. 



b. Joined in rings, Syncyclia. 



B. Surrounded by membranous tubes. 



a. Tubes separate. 



a. Frustules strait, Naunema* 



b. " curved, Gloenema. 



b. Tubes joined. 



a. Fasciculate, ....... Schizoncma.* 



b. Branching, Micromega. 



The genera marked thus (*) have been detected in the United Stales. 



Ehrenberg remarks of this family, that " the organization is difficult 

 to recognize, 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 ditferences observed in the 

 forms of the carapace have been made use of in classifying them, 

 (see preceding table.) In several genera, are found internal hyaline 

 vesicles of variable form ; these are colorless, and resemble the stom- 

 achs of the Polygastrica, and in recent experiments they have been 

 colored by means of indigo. The female organs are colored or color- 

 less granules, forming two or four groups, which are placed near the 

 middle of the body, as in Navicula, Cocconema, Naunema, &c. These 

 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, 

 &c. ;) at other times they appear under the form of a tube enveloping 

 the stomachs and other organs, (Xanthidium, Euastrum, Micrasterias.) 

 The 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 almost every 

 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 bu 

 found in great quantities among the filiform Algae, which they 

 often invest completely with their crystalline carapaces. 



