39 30 Proceedings oj the Royal Irish Academy. 



Piona rotunda (Kramer). 



Doo Lough and Carrownisky Eiver near Louisburgh ; Garranbawn Lough 

 near Ballynakill. 



Much less common in the Clare Island district than the following species. 

 The number of acetabula present in the female varies from about 18 to 23 on 

 each plate. 



Piona rotundoides (Sig. Thor). (Plate III., fig. 33 a-b.) 



Loughs Cahasy and Lugaloughaun near Louisburgh ; Lough Conn ; 

 Glendalough Lake, Connemara ; lakes near Clifden. 



A Piona which agrees well with Thor's description (26) of the present 

 species is widely spread in Irish waters, being especially abundant in the 

 larger lakes of the west of Ireland. At Lugaloughaun a deep sub-alpine lake, 

 this species and Hygrobates naicus were the only water-mites found. 



The chief character by which it may be separated from P. rotunda Kramer 

 is the greater number of discs on the genital plates. The latter are larger than 

 in rotunda ; the Irish specimens that I have examined carry from twenty-eight 

 to thirty-five discs on each plate, and occasionally as many as forty (PL III., 

 fig. 33 b). In addition to these there are from two to six discs lying free 

 between the plates on each side. The hair-bearing pores on the lower extremity 

 of each plate are arranged in a row close to its margin. In the male the 

 genital plates are also larger and carry more discs than the allied species 

 (PI. III., fig. 33a). 



Distribution. — Scandinavia (Thor); Great Britain (Norfolk Broads, &c, 

 Soar) ; Ireland. 



Piona rufa C. L. Koch. 

 Common in lakes at Westport and Louisburgh. 



Piona paucipora (Sig. Thor). (Plate III., fig. 34.) 



Lough Conn, June, 1903. 



A number of examples were collected in this, the only known Irish locality, 

 by Mr. W. F. de V. Kane. 



Piona paucipora is closely allied to Piona rufa, but may be easily distin- 

 guished from that species by the structure of the genital area ; the colour of the 

 mite is yellowish, with dark blotches on the upper side. 



In the male there are about ten genital discs ; one of these lies free within 

 the genital plates. The latter are sickle-shaped and are very characteristic of 



