HYDRACHNA. HYDRACHNA. 
Generic Character. 
Caput, thorax, et abdomen 
unita. 
Palpi duo, articulati. 
Oculi duo, quatuor, sex. 
Pedes octo, natatorii. 
Head, thorax, and abdomen 
united or connate. 
Feelers two, jointed. 
Epes two, four, or six. 
Legs eight, formed for 
swimming. 
T ^> 
HE genus Hydrachna, allied in the closest 
manner to that of Acariis, under which the only 
species known to Linnaeus were arranged, was 
first instituted by the ingenious Muller, by whose 
industrious researches many new and curious kinds 
have been discovered. 
Among the larger insects of this genus is the 
Hydrachna fiacclda^, well described . by Degeer 
and others. Its size is that of a small pea, and its 
colour a very bright red: its shape is nearly glo- 
bular, but the skin is of such a nature as to yield 
to every inclination of the body, so that the whole, 
when taken out of the water, has an irregularly 
* I give it this name in order the more clearly to distinguish 
it from one or tw^o others with w^hich it may sometimes be con- 
founded. 
