350 



entrance of water effectually prevented. This motion is sometimes so 

 sudden as to retain, between the body and elytra, a small quantity of un- 

 imbibed air, which makes its way under the tips of the latter, where, as the 

 insects sinks, it adheres, a transparent globule, brilliant as quicksilver. The 

 upper surface of the body being arched or convex, and its under side braced 

 by a breastbone of several pieces firmly interlocked, it is rendered suffi- 

 ciently strong and inflexible ; while its oblong oval form and thin margins 

 are well adapted for its rapid and varied motions. 



Although insects have no organs of voice most of them emit various 

 sounds; and those of this family, in common with many others, exhibit 

 their distress on being handled by a creaking sound produced by the friction 

 of the tail against the elytra. 



They pass the winter in the perfect state, burrowing in the banks and 

 mud of their pools. 



One has been kept for three years and a half in perfect health, in a glass 

 vessel filled with water, and supported by morsels of raw meat. It was 

 capable of fasting a month; was very sensible of the changes of the 

 weather, which it indicated by the height at which it remained in the vessel. 



DeGeer fed one upon flies and spiders, and, after it had lived a long time, 

 he gave it a large leech which it attacked and devoured ; but it paid dear 

 for its gluttony; the food proving indigestible was thrown up the next day 

 with great efforts, and shortly afterwards the insect died. 



GENUS DYTISCUS. 



D. *fraternits. Punctured; beneath black; thorax with a yellowish band 

 and margin; coleoptra arcuato-fasciate behind; elytra of the female 

 sulcated. 



Length about eleven twentieths, breadth between six and seven twen- 

 tieths of an inch. 



Body depressed, with numerous somewhat dilated punctures. Head pale 

 rufous, black at base, with two lunated piceous spots between the eyes. 

 Thorax with an ochreous yellow margin, and transverse band, which is 

 dilated backwards at the sides, and separated from the posterior margin by 

 an obsolete blackish line. Scutel impunctured, black. Coleoptra blackish 

 from numerous confluent, black spots and flexuous lines; epipleura, exter- 

 nal margin, subsutural line, common arcuated band behind the middle, and 

 obsolete macula at tip pale ochreous yellow. (Male with four obsolete 

 elevated lines on each elytron.) Prosternum and anterior legs pale ochre- 

 ous; hind legs piceous, thighs black. Ventral segments with a pale piceous 

 submargin, and, on each side, a yellowish spot. 



Female. Coleoptra with eight, dilated, hairy grooves; (not including the 



