2 2 University of Michigan 



ing to three species, A. signata (Fieber), A. intcrnipta (Say)^ 

 and a new species to which he gave the name A. nana; but 

 the entire collection was not determined. After examining 

 the 1918 collection, I strongly suspect that several other spec- 

 ies are represented in it, but I have not attempted to make any 

 determinations in this very difficult group ; and, as Professor 

 Abbott is now in Japan, identification of these forms by a 

 competent authority is not possible at present. Of A. itana 

 Professor Abbott wrote in 191 3, "It belongs to the Arctocorixa 

 intcrrupta group, and is the smallest member of it that I have 

 seen." No description of this species has been published as 

 yet. 



Arctocorixa intcrrupta is the most abundant water boatman 

 in this vicinity, with A. nana second and A. signata third, the 

 three species occurring in the 1918 collection roughly in the 

 ratios 3:2:1 respectively. The other forms were relatively 

 uncommon. 



Discussion 



The general characteristics of the hemipterous fauna of this 

 region can be summarized very briefly. As far as can be 

 judged from the study of the limited area under consideration, 

 the fauna of this part of ]\Iichigan is transitional between that 

 of the north and north-west and that of southern Michigan — 

 and the latter appears to be fairly typical for central North 

 America. Careful collecting at Douglas Lake failed to show 

 the presence of Benacns griscus, Pclocoris femoratiis, Ranata 

 kirkaldyi, or Gelastocoris, all of which are fairly common in 

 the region about Ann Arbor ; while Plea striola, whicli is very 

 abundant at Ann Arbor, was found to be uncommon here. On 

 the other hand, a few boreal species such as Notonecta insul- 

 ata and Gerris rufoscutellatus, which occurred at Douglas 

 Lake, are rare in the south-eastern part of Michigan. The 



