Clare Island Survey — Acarinida. 39 81 



Metaparasitidae and the very interesting Rhodacaridae 1 in which the male 

 genital foramen is placed in the sternal shield at a little distance from its 

 anterior margin, thus forming a link between Berlese's two main groups of 

 the Gamasoidea. There would appear, however, to be some doubt that this 

 is true of the first-mentioned family, as Berlese considers Metaparasitus to be 

 identical with Gamasolaelaps, and the male foramen is in the usual frontal 

 position in that genus. On this account, the family Metaparasitidae is 

 omitted from the following table, which now numbers ten families : — 



1. Male genital foramen placed in the sternal shield, . . .2 



— Male genital foramen on the anterior margin of the sternal shield . 5 



2. Female genital foramen large, protected by a chitinous plate 



enclosed in the sternal shield. 2 Leg pits (fossidae pededes) present 

 in many genera, ..... Uropodidae. 



— Female genital foramen a transverse incision between the sternal and 



genital plates. Leg pits absent. Parasitic on arthropods. 



Antennoplwridae. 



3. Sternal shield entire, two dorsal plates present in both sexes, peritreme 



ventral, ...... Zerconidae. 



— Female with two, paired, sternal shields (fused in male), and 



three dorsal plates, peritreme dorsal, Thinozerconidae n. fam. 



4. " Body divided into two distinct regions : a true thorax and a true 



abdomen " (Oudemans), male genital foramen in the sternal shield 

 near its anterior margin, .... Pdiodacaridae. 



5. Female genital shield entire (Laelaps), or, only partly divided in the 



middle line (Gamasus) . . . . . .6 



— Female area genitalis formed of two hinged lateral plates, . .10 



6. Male with second legs much thicker than in the female ; femur, 



patella, and tibia more or less armed with processes, Gamasidae. 



— Second leg not, or but little, thickened in the male, . . .7 



7. Adults well chitinized and free living (a few species of Laelaps are 



parasitic on rats, mice, and voles) , . . . Laelaptidae. 



— Adults less chitinized, entirely parasitic on vertebrates, . . 8 



8. Stigma dorsal, ..... Pteroptidae. 



9. Stigma ventral, ..... Dermanyssidae. 

 10. A post-anal plate is present, .... Celaenopsidae. 



1 The type species, Rhodacnrus roseus Oudemans, occurs in Ireland. I have found the adult female 

 under stones, amongst dead leaves, in the Tolka Valley, near Dublin, during the month of February. 

 As far as I am aware this is the first record of its occurrence since Oudemans described it from the 

 Netherlands (74, p. 42). 



- In a few forms of the Uropodidae belonging to the genera Uroseius, Trachytes, Celeano, and 

 Polyaspis the female genital foramen is not enclosed in the sternal shield. 



