MITE'S OF SUBFAMILY HAEMOGAMASINAE — KEEGAN 239 



ticus at North Bull, County Dublin, Eire. After comparing these 

 specimens with those taken from nests of mice in England, he con- 

 cluded that these mites from Eire represented the form described 

 by Berlese and that because of their morphological differences from 

 korridus their restricted habitat in nests of voles and field mice, and 

 their distribution in Eire and the Mediterranean area, they represented 

 a distinct species. 



In addition to the diagnostic features of arvicolancm given by 

 Berlese, Turk included the following points : Length of female 1,300/i; 

 sternal shield as in horridus; genito ventral shield as in H. nidi rather 

 than horridus in being flask-shaped and somewhat expanded pos- 

 teriorly, rather than with almost straight lateral margins and a trun- 

 cate posterior margin; anterior portion of shield with two pairs of 

 setae; anal shield larger than in horridus and with 14 setae; chelae 

 of female stronger and more elongate than in horridus; chelae of male 

 differ in some respects from those of horridus; average length of 

 male l,200fi. 



I have seen no male specimens of horridus or of arvicolarum^ but 

 through the kindness of Dr. Turk I was able to examine four female 

 specimens of arvicolarum taken from the type locality and habitat. 

 Two of these were engorged, but morphological details of the others 

 were distinct. 



These specimens lack distinctly enlarged terminal body setae ; chelae 

 are slightly more elongate than those figured by Michael and Oude- 

 mans, or of the four specimens of horridus examined; anal shield is 

 relatively large; distinctive in possessing 35 and 39 accessory setae 

 on the genitoventral shield and in having the sternal shield slightly 

 wider than long. Although the genitoventral shield of one specimen 

 is expanded posteriorly, that of the other possesses relatively straight 

 lateral margins and a truncate posterior margin. 



Morphological variations, individual as well as among local popula- 

 tions, are indicated in the published descriptions of horridus. Varia- 

 tions in numbers of anal setae and in occurrence of smooth and barbed 

 body setae have been discussed. Of four specimens typical of hortidus 

 from Katece, Yugoslavia, two possess flask-shaped genitoventral 

 shields and two possess the truncated posterior margin and more nearly 

 straight lateral margins. 



In my opinion structural differences such as those by which arvi- 

 colarum was separated from horridus by Berlese and Turk are not 

 suflficient in themselves to warrant specific or subspecific status. 

 Studies of morphological variation of horridus throughout its range, 

 including Eire, will be necessary before the taxonomic value of such 

 characters can be determined. 



