THE ROMANCE OF NATURAL HISTORY. 



a little active genus,* which, being wholly with- 

 out the foot common to this class of animals, is 

 always found swimming, being apparently inca- 

 pable of resting, or, at least, of crawling. The 

 group contains many species, and most of them 

 have their shells ornamented with some symmetri- 

 cal variation of the surface. In one,f a ridge 

 runs down the middle of the back, dividing the 

 shell into two equal lateral portions, each of 

 which is subdivided into about ten polyhedral 

 areas by intervening ridges, of which no two are 

 alike in form, though each corresponds accurately 

 with its fellow on the opposite side. The form of 

 each area is constant in every individual. In 

 another,! the medial line is occupied by five areas, 

 of which the first is an imperfect hexagon, the 

 second is square, and the posterior three are 

 hexagons; from the salient angles, other ridges 

 run off sidewise, and form other imperfect poly- 

 gons. In others,§ the division is into many hexag- 

 onal tesselations, varied with other forms in the 

 outer or hinder areas according to the species, 

 and having the peculiarity that the dividing ridges 

 are well-defined narrow elevations armed through- 

 out with conical points in single row. 



I may be accused of exaggeration in presuming 

 all these creatures to be seen in one drop of water. 

 I do not pretend to be depicting them from one 

 single actual observation ; at the same time I may 

 say that I have described nothing but what I 

 have personally observed ; and I have known 

 many small pools and other collections of water 

 sufficiently rich in organic life to afford examples 

 of quite as many species as I have enumerated, 

 aye, and many more, in a single dip taken at ran- 



* Anurcea. + A. tecta. X A. curvicornis. 



§ A. acideata, serrukita, &c. 



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