176 DESCRIPTION OF [Polygastrica. 



so that the numerous illustrations of this family, whether 

 the members be considered as animal or vegetable, will, 

 I believe, be highly acceptable both to the botanist and 

 naturalist. 



In this family we are not only presented with the sim- 

 plest forms of organic matter, but, from their numbers and 

 the indestructibility of their shells, they have led to many 

 important discoveries. The large masses of meteoric 

 paper which fell in 1686 have recently been shewn to 

 consist mainly of their coverings, while several hundred 

 square feet of a flannel-like substance, lately found near 

 Sabor, in Silesia, after an inundation, was composed of 

 Fragillaria, Navicula, Cryptomonas, and Closterina, inter- 

 woven with Conferva rivularis. 



As microscropic objects, the markings of the fossil 

 species are highly interesting ; and when mounted as 

 opaque objects, a verification of the structure of their shell 

 is clearly demonstrated. 



The English specific names are taken from the German. 

 In the Natural History of Animalcules, I have taken them 

 from the Latin ; this will account for the non-agreement. 



The grand divisions of this family are into single and 

 double-loricated animalcules ; the genera comprised in the 

 first being separated into those which are attached to a 

 pedicle or stalk, and those which are destitute of such 

 appendage, or free. 



