28 One Thousand Objects 



following descriptions in such a sense. Fresh, brackish, 

 and salt water are alike inhabited by various species, and 

 their flinty skeletons are found buried in the earth in a kind 

 of fossil condition, in deposits sometimes of miles in extent, 

 which often indicate the bed of some ancient lake. When 

 collected in a living state, floating on the surface of ditches 

 or adhering to larger plants, they are, besides their own 

 endochrome, usually mixed with organic matter, from which 

 they must first be cleansed. This is usually accomplished 

 by boiling in nitric acid, which destroys all but the flinty 

 skeletons ; and when thoroughly cleansed, by washing in 

 distilled water, from all trace of acid, these skeletons are 

 mounted dry or in balsam. The surface of the valves are 

 marked in various ways with channels, stria?, ribs, or dots; 

 and the form of the valves is almost as variable as their 

 markings. For the following enumeration of the species 

 most commonly found in fresh and also in salt water, we 

 are indebted to Mr. Frederic Kitton, of Norwich, a 

 gentleman well known as an authority, and of great 

 experience in this subject. 



198. ROBUST EPITHEMIA (Epithemia turgida). The 

 group or genus to which this belongs contains species 

 which are parasitic, adhering by the concave surface to 

 the stems of small aquatic plants and alga. The valves 

 are arched or bent (arcuate), and crossed by transverse 

 ribs. This species is the most robust of those common 

 in fresh water, and the ribs are very distinct. Common 

 in ditches. (PL III., fig. 26.) 



199. MARSH EPITHEMIA (Epithemia rupestris). The 

 present is a small form, with almost spindle-shaped valves, 

 which are slightly curved, with the ribs distant from each 

 other, and the striae between them faint. Marshes and 

 boggy pools. 



200. SWOLLEN EPITHEMIA (Epithemia gibba). This 

 species differs conspicuously from the preceding, the front 

 view being straight, or line-like, swollen at the middle and 

 at each end. The side view is narrow, with straight 

 parallel sides and obtuse ends. Marshes and boggy 

 pools. 



