272 CD. SOAR ON THE GENUS HYDRACHNA. 



genus Hydrachna, others have been added to such an extent that 

 the modern genus of this name includes more species than the 

 total number of mites mentioned by M tiller in 1781. 



Hydrachna is perhaps not so interesting as some of the other 

 genera because its species exhibit no great variety of colour, 

 being nearly all more or less red, ranging from an orange-red to 

 a blackish red, or black and red as in Hydrachna geographica. 

 There is also no variety in the external structure, and no obvious 

 sexual differences occur except in the genital area, whereas in 

 some of the other genera we find a great deal of variation in 

 external structure, the males and females often being very 

 different in appearance. * 



The species of the genus we are now considering vary very 

 much in size, Hydrachna geographica, the giant of the whole 

 family, being as much as 8 mm. in length, whilst others measure 

 as little as 1 mm. The swimming hairs on the legs vary slightly 

 in number and in length. Some of the species of Hydrachna are 

 fairly common, and where found are generally taken in great 

 numbers. The Norfolk Broads district is the most prolific 

 hunting-ground known to me as regards the number of species 

 found. With the exception of 'Hydrachna globosa very little is 

 known concerning the life-history of these creatures ; and having 

 dealt with this portion of the subject in a previous contribution I 

 shall refrain from further reference to it in the present paper. 



Generic Characters. 



Body soft-skinned, usually papillated, with or without chitinous 

 plates between or behind the eyes. Median eye always present. 

 Rostrum projected forward nearly as far as palpus. Epimera 

 forming four distinct groups. Swimming hairs present on legs. 

 Claws on all feet. Genital area heart- or pear-shaped. No 

 sexual distinction except in genital area. 



With the exception of one species, Hydrachna levigata, Koen., 

 all have a more or less papillated skin on the body part. These 

 papillae assume various forms in different species. They may be 



