HYDRADEPHAGA. 67 



Gyrinus bicolor (Plate III, Fig. 6), the narrowest and 

 most elongate of our " whirlwigs," is found plentifully 

 in brackish water at Southend, and elsewhere on the 

 coast. 



Orectochilus villosus, one of this family, differs from 

 the others in being hairy: it is supposed to be less 

 gregarious than the true Gyrini, though instances occur 

 when it is found in great numbers. Unlike the light- 

 loving whirlwigs, it hides itself in banks by day, and 

 mostly performs its evolutions on the water by dark. 

 Its larva forms a white silky cocoon, which has been 

 found under willow-bark, and in a freshwater shell. 



Good Latin descriptions of most of our Hydradephaga 

 will be found in Eriehson's ' Kafer der Mark Branden- 

 burg' ; and M. Aube's ' Species Gen. des Hydrocan- 

 thaires et des Gyriniens/ published at Paris in 1838, 

 comprises all the then known species in this subsection. 



