MITES OF SUBFAMILY HAEMOGAMASINAE — KEEGAN 233 



of these surfaces except by indicating distances of setae from one an- 

 other. This was found to vary from as little as 4/x to 15/x to as much 

 as 30)u to 60/i. More numerous setae on the dorsal shield and dorsal 

 and ventral body surfaces were usually associated with larger num- 

 bers of setae on genitoventral and anal shields. In general, setae of 

 these surfaces were more numerous on western specimens. 



Numbers of genitoventral setae : Varied from 12 to TO in a series 

 of 104 specimens examined; the mean was 31. Larger numbers were 

 usually found on western specimens. Of 39 specimens with more 

 than 30 crenitoventral setae, all but five were taken in western States. 

 However, third from the top of the list with 60 setae is a specimen 

 from New Hampshire. Of the 65 specimens with less than 31 setae, 

 only seven were taken in western States. 



Numbers of anal setae : In a series of 88 specimens numbers of anal 

 setae varied from 3 to 8 ; the mean was 5.6. Although larger numbers 

 were usually associated with more numerous genitoventral setae, this 

 was not always the case. Examples of such disparity are shown m the 

 following combinations: 20 genitoventral setae with 7 anal setae; 29 

 genitoventral setae with 7 anal setae; 55 genitoventral setae with 

 5 anal setae ; 45 genitoventral setae with 6 anal setae. Larger nmnbers 

 were found most often on western specimens. 



Length-width ratio of sternal shield: In seven European speci- 

 mens of E. amluUns the length- width ratio of the sternal shield varied 

 from 1.2 : 1 to 1.7 : 1. In 76 North American specimens this ratio 

 varied from 1.3 : 1 to 2.4 : 1. In general, lower ratios were associated 

 with larger numbers of setae. This ratio in most cases represents a 

 variation in the margin separating the presternal area and the sternal 

 shield proper rather than in position of pores and setae. In specimens 

 with higher ratios the anterior pair of sternal setae is on the anterior 

 margin of the shield rather than slightly posterior to it. 



In addition to variations previously discussed. North American 

 specimens show slight variations in details of structure of the posterior 

 end of the peritreme and in presence or absence of a basal seta on the 



fixed chela. . . 



An attempt to separate specimens of this series into distinct species 

 on the basis of possession three, five, or eight anal setae would necessi- 

 tate separation of specimens from single lots or from identical hosts 

 and localities into several species. It is my opinion that, since the 

 concept of constant seta number upon which H. reidi, H. twitcheUi, E. 

 onychomydis, E. oregonensis, and E. scmrovterl were described has 

 been demonstrated to be erroneous, these species are one and, lacking 

 further means of distinction, should be considered synonymous with 



E. ambulans. 



DistHhution.-R^VOvi^^ from Greenland by Thorell (1872) ; Siberia 

 by Koch (1878) ; Great Britain by Michael (1892), Hirst (1914), and 



