nVDRACIlNA. 
46(j 
flaccid appearance: this is most remarkable in the 
full grown animal, which is also of a much more 
torpid nature than the rest of the genus, which 
are animals of great celerity of motion; and in- 
deed the jmung or unadvanced individuals of the 
present species are of a more compact appearance, 
and swim with a greater degree of swiftness than 
the larger ones. The H: flaccida is not very un- 
eommon in stagnant waters. 
Of all the Hydrachnae yet discovered by far the 
most elegant is the Hydrachna geographica, so 
named from the fancied map-like distribution of 
its variegations. It is one of the largest of the 
genus, equalling the si^ie of the former: it is oc- 
casionally seen in clear ponds and other stagnant 
waters, but is one of the rarei^inds: its shape is 
globular, and its colour a polished black, decorated 
wdth carmine coloured spots and patches, which, 
in a certain light, are accompanied by a kind of 
gilded lustre: four round spots of this colour are 
situated on the middle of the upper part of the body, 
and are bounded by four large, angular patches; 
besides which, on the sides and lower part of the 
body, are some others: the legs are varied with 
black and red, and, as in the rest of the genus, 
beautifully ciliated with long hairs. This insect 
swims with great celerity, and appears in almost 
constant motion. When seen in its state of per- 
fection, it may be numbered among the most 
beautiful of the British insects. 
flydrachna Roeseliana. I name after the inconi- 
