BRITISH HYDRACHNID^. 273 



similar teeth. The pointed projection or prickle, directed forward, 

 which is set upon the point of the fourth joint, and which some- 

 times attains a length half as long as the fifth joint, appears, on 

 the other hand, peculiar to this genus. Another and more essen- 

 tial difference between Nescea and Fiona appears in the formation 

 of the ' fold of generation,' for in the case of the last named this 

 has about the same form as in the case of Limnesia and Hygro- 

 bates ; that is to say, the crevice is surrounded on either side by 

 three stigmata only, while the genital fissure in Nescea has numer- 

 ous smaller ones on each side, which are quite different in shape 

 to these." 



It will therefore be seen that there are two very important 

 features in which Fiona differs from Nescea, namely, the pointed 

 projection or prickle on the edge of the fourth joint, which partly 

 overlaps the fifth joint (see PI. XII., Fig. 2, and the three genital 

 pores on each side of the genital crevice (Fig. 3). These two very 

 distinctive features, I think, are sufficient to warrant Koch in sepa- 

 rating the mites which bear these peculiarities from the genus in 

 which he had originally placed them. 



In the extract given above from Neuman, the reader will 

 notice two more genera mentioned — namely, Limnesia and Hygro- 

 bates, neither of which we have at present considered ; but we 

 shall come to them later on, when those interested in these crea- 

 tures will be able to compare the drawings of the genital area one 

 with another, and see how near the similitude is. That Neuman 

 himself was satisfied with the separation of this genus from Nescea 

 is proved by his adding five species to the list. 



Genus V. — Fiona. 



1842. — Fiona, C. L. Koch, Ubersichi des Arachnidensy stems, 

 Heft 3, p. 13, Tab. i, Fig. 4. 

 Body soft. All tarsi have claws. Legs have swimming hairs. 

 Palpi not pincer-shaped, but on the anterior margin of the last 

 joint but one is a short, peg-like appendage near the fifth joint. 

 On each side of the genital crevice are three pores only. Eyes 

 wide apart. Mandibles in two distinct portions ; Epimera forming 

 two groups on each side. 



