1902-1903.] Fresh - Water Mites. 43 



B, ventral surface of male ; C, dorsal, D, ventral surface of 

 female). Here you will see how great is the difference in 

 structure between the sexes. The males of a great number 

 of the Arrhenuri have also a peculiar spur on the fourth 

 segment of the fourth leg. They do not all have this. There 

 is also a depressed line on the dorsal surface of both male 

 and female. In Great Britain we have had recorded a large 

 number of this genus by Dr George of Kirton-in-Lindsey in 

 the pages of ' Science Gossip,' and in his list of Hydrachnids 

 of Lincolnshire. Arrhenurus caudatus has been found in the 

 Upper Elf Loch by Mr Williamson (Aug. 1900). 



Arrhenurus globator, Miill. (Plate III. fig. 2 : A, dorsal, B, 

 ventral surface of male; C, dorsal, D, ventral surface of 

 female), is a very common mite in England, but I have not 

 yet heard of it having been found in Scotland. Here again 

 we find the spur on the fourth segment of the fourth leg. 



Arrhenurus claviger, Koenike (Plate III. fig. 3 : A, ventral, 

 B, dorsal surface ; C, petiolus). A brilliant red mite, with 

 the horns I spoke of and the petiolus between. The legs 

 have not been drawn, but they are similar to fig. 1 and fig. 2. 



Arrhenurus nodosus, Koenike (Plate III. fig. 4, dorsal sur- 

 face of male). This will give you an idea of the third form I 

 mentioned. 



The next genus is Brachypoda, Lebert, which contains only 

 one species. This genus was previously known as Axona. 

 The only known species is versicolor, Miill. (Plate IV. fig. 1 : 

 A, dorsal, B, ventral surface of male ; C, dorsal, D, ventral 

 surface of female). It is a very small and common mite, and 

 when first caught is brilliant in colour. Here again we find 

 the spur on the fourth leg. It is also hard-skinned. It has 

 been found in Scotland by Mr Taverner and Mr Williamson. 

 When taken, as a rule it is found in large numbers. 



Midea orbiculata, Miill. (Plate IV. fig. 2 : A, dorsal, B, 

 ventral surface of male ; C, dorsal, D, ventral surface of 

 female). This is another genus with only one known species. 

 It is the most brilliant mite I know of when taken in good 

 condition. The male is without the spur on the fourth leg, 

 but it has a peculiar formation of the tarsus of the third leg. 

 I have taken a number of this species in England, but I do 

 not think it has yet been found in Scotland. 



