North American Centropagidce. 233 



inner apical angle. Second segment sub quad rate, about one 

 and a half times as long as wide ; armed at the outer apical 

 angle with a plumose spine almost twice as long as the seg- 

 ment, and on the inner margin with a few fine hairs. Third 

 segment slightly longer and narrower than the preceding; 

 irregularly triangular, with sulcate margins and truncate 

 apex ; armed on the outer margin with two long, slender, plu- 

 mose setae, at the apex with two similar setae and a short 

 smooth spine, and on the inner margin with one seta similar 

 to those already mentioned and one shorter lamellate seta, 

 and provided on the upper half with a few tine hairs. 



Length of female, 1.703 mm.; that of male, 1.362 mm. 



The above description was prepared from specimens col- 

 lected in the summer of 1896 at the Illinois Biological 

 Station, at Havana, 111. ; from type specimens; and from 

 other State Laboratory material collected at various times 

 and places, mostly in Illinois. 



The single species of this exclusively North American 

 genus was first described by Herrick in a paper read before 

 the Minnesota Academy of Sciences in 1879, but which, 

 owing to a fire, was not published until 1882. The descrip- 

 tion then appeared, under the name Potomoichetor fucosus, in 

 the Tenth Annual Report of the Geological and Natural 

 History Survey of Minnesota (Herrick '82). This Report 

 was not distributed, however, until after the August number 

 of the "American Naturalist" appeared, which contained the 

 description of Osphranticum labronectum by Forbes ('82). 



De Guerne and Richard, in their "Revision" ('89b), pub- 

 lish the best figures of this species. Although not strictly 

 correct in every particular, the omissions are of minor im- 

 portance, as may be seen by the following enumeration of 

 them. In the fifth legs of the female the hair on the second 

 basal segment, the small spines at the outer apical angles of 

 the segments of the outer ramus, the hairs on the outer 

 margins of these segments, and the lamella of the hook at 

 the inner apical angle of the second segment of this ramus 

 are not figured. The third segment of the inner ramus is 

 not quite correct. Here the hairs on the inner margin, the 



