1906-1907.] British Hydrachnidce : The Genus Piotta. 391 



Genital plates disc-shaped, acetabula nearly one size, and fi'om 

 18 to 24 on each plate, numerous small hairs round outer 

 curve of genital lips .... 14. Fiona camea ? 



Genital plates elongated, having from 10 to 15 acetabula, one or 

 more being larger than others on each plate 22. Fiona elegans ? 



8. Genital plates tongue-shaped, with about 30 acetabula all one 



size on each plate 9. Fiona fallax ? 



Genital plates tongue-shaped, with from 20 to 25 acetabula. 



18. Fiona stjOrdalensis ? 

 Genital plates tongue-shaped, with from 25 to 35 acetabula each, 

 2 acetabula on each plate being larger than others. 



12. Fiona nodata ? 



MALE. 



1. With acetabula entirely free, none on special plates. 



21. Fiona adimcopalpis $ 

 With one or more acetabula free, remainder on special plates. 



19. Fiona paucipora ^ 

 With all acetabula on special plates 2 



2. With cherry-shaped seminal pocket . . . . . . 3 



With trefoil-shaped seminal pocket 4 



With small seminal pocket, more or less pointed at each end . 5 



With heart-shaped seminal pocket 6 



With reniform seminal pocket, much broader than long. 



3. Fiona Neumani $ 



3. With 9 swimming-hairs at distal end of each patella. 



14. Fiona camea ^ 

 With 3 swimming-hairs at distal end of each patella. 



16. Fiona circularis $ 



4. With 6 or 7 swimming-hairs at distal end of each patella, and 



corkscrewlike claw on third tarsus ; two acetabula larger than 

 others on each genital plate , . . 12. Fiona nodata $ 



With 5 swimming-hairs at distal end of each patella, and smaller 

 claw than P. nodata on third tarsus ; anus almost within the 

 bay of genital plates . . . .18. Fiona stjSrdalensis $ 



With 5 swimming-hairs at distal end of each patella, and anus 

 well outside the bay of genital plates ; claws short and close to 

 tarsi 20. Fiona uncata $ 



With only 3 hairs at distal end of each patella 1. Fiona fuscata $ 



5. With 2 hairs at distal end of each patella, and anus on genital 



plate ; outer edge of genital plates extending along margin of 

 posterior epimera as far as fourth leg 10. Fiona discrepans $ 



With 3 swimming-hairs at distal end of each patella, and anus on 

 genital plate 17. Fiona conglobata $ 



