39 80 Proceedings of the Royal Irish Academy. 



Zercon trigonus Berlese (PL VI, fig. 25). 



A single example of this beautifully formed mite occurred amongst 



moss sent from Birr, in King's County, during November. It may be 



distinguished from the preceding species by the circular pits on the dorsum, 



and by the crenulate hinder margin of the body. Berlese found it amongst 



mosses in Italy (6). A sketch of the dorsal surface is given in the present 



paper. 



Epicrius geometricus Can. et Fanzago. 



Found amongst moss from Knappagh Wood, near Westport, in August. 

 Distribution. — A widespread European species, has been recorded from 

 Germany, Holland, Italy, and Britain (Lincolnshire, Dr. George). 



Asca affinis Oudemans. 



Nymphae, apparently referable to this form occurred abundantly in a 

 sand-pit used for macerating bones, Dublin. 



Family THINOZEBCONIDAE, n.fam. 



On the coasts of Mayo and Dublin I have found between tide-marks both 

 sexes of an acarid, which does not appear to have been previously observed. 

 This interesting form clearly belongs to the Gamasoidea ; yet its structural 

 characters are such that it is not possible to refer it to any one of the 

 described genera, and I believe it should also be regarded as the type of a new 

 family allied to the Uropodidae and the Zerconidae. Affinities with the last- 

 named family are apparent in the arrangement of the sternal and ventro- 

 anal shields in the male, in the position of the male genital foramen 

 it resembles both of these families. 



The presence of two paired, sternal shields in the female is possibly the 

 most remarkable characteristic of the present genus. Berlese has described an 

 exotic form, Heterozercon, in the female of which there are two small sternal 

 plates, however, the two forms are otherwise quite distinct. The dorsal position 

 of the peritreme is also very remarkable. Asa matter of fact there is scarcely 

 room for the peritreme on the ventral surface of the body owing to the wide 

 sternal area, the unusually large size of the acetabula, and the presence of 

 outer pedal plates. The spine armature of the legs is remarkably varied. 



Iu order to indicate the position of the family Thinozerconidae I have pre- 

 pared a synoptical table of the known European families which is necessarily 

 based on Berlese's " Conspectus familiarum " (2, p. 15) in which he recognizes 

 two main divisions of the Gamasoidea differing in the position of the male 

 genital foramen. 



Dr. Oudemans has described two additional European families, the 



