380 BritisJi Hydrachnidce : The Genus Piofia. [Sess. 



60 acetabula each, and one or two free on the ventral surface 

 within the curve of each plate. It is rather a rare species, 

 having only been found at Chesham and Sevenoaks up till the 

 present. The male is, as yet, unknown in Britain. (Plate 

 XXXIL, figs. 17, 18.) 



6. Fiona rotundoides, Sig Thor. 



This is another variety of the group with sickle - shaped 

 genital plates. It is a much larger species, measuring as 

 much as 1*80 mm. in length. Genital plates with from 30 

 to 40 acetabula on each plate. Colour, a pale yellow, with 

 very dark markings, which are very regular in their arrange- 

 ment. It is a rate mite, having only been found at Earlswood 

 and on the Broads. 



3Iale. — About 0"96 mm. The genital plates are larger than 

 those on P. rotunda, Kram., and have from 30 to 35 acetabula 

 on each plate. The plates also project further beyond the 

 posterior points of the fourth pair of epimera. (Plate XXXII., 

 figs. 19, 20 ; Plate XXXIIL, figs. 30-32.) 



7. Fiona rotunda, Kram. 



Female. — About same size as P. obturbans. Pier., I'lO mm. 

 in length. Colour yellow, with brown markings on the dorsal 

 surface. Malpighian vessel very distinct. Legs long and 

 rather thin, well supplied with swimming-hairs ; claws rather 

 prominent; colour of legs pale yellow. Palpi strong, and 

 nearly twice as thick as trochanters of first pair of legs. 

 There are two hair pegs placed very near one another on the 

 flexor edge of palpi. The genital plates are sickle-shaped, 

 with from 15 to 20 acetabula on each plate, and some free on 

 the ventral surface within the curve of each plate. 



3Iale. — About 0*80 mm. long, of same colour as female, but 

 very often darker in tone. The seminal pocket is very small 

 and pointed at each end. It can easily be recognised from 

 the male P. obturbans by the anus being some little distance 

 behind the plates instead of being placed within the bay. 

 This can be more easily understood by comparing figs. 24 and 

 27, Plate XXXIII. Each plate has from 24 to 30 acetabula. 



