PROC. ENT. SOC. WASH., VOL. 23, NO. 9, DEC., 1921 199 



related to A. oculatus just described, but differs from it in having 

 small pseudoculi, which are more lateral in position, in having 

 the head more slender and in minor details. The species is very 

 common at the locality where it was taken. 



Acerentuloides, n. gen. 



The thorax and at least first abdominal segment without tergal plates and 

 tergal apodemes; tergal plates present on some of the posterior abdominal 

 segments, without transverse lines. Most of other characters similar to those 

 of Acerentulus. 



Type. Acerentuloides bicolor Ewing. 



The type species of this genus is minute and has the anterior 

 part of the body hyaline and but little chitinized but the pos- 

 terior part well chitinized. It differs from the species of 

 Acerentulus known to the writer in many characters, but at 

 present it can not be stated how many of these should be 

 regarded as generic. 



Acerentuloides bicolor, n. sp. 



Minute species with head, thorax and anterior parts of abdomen whitish, 

 while the posterior part of the abdomen is yellow. Head long; pseudoculi 

 lateral; rostrum short, minute. Exposed part of prothorax about three times as 

 broad as long. Meso-, and metathorax about equal, hyaline without tergal or 

 sternal plates. First two abdominal segments without tergal plates, the remain- 

 ing segments showing a progressive increase in the development of these plates 

 from the third segment backward; seventh abdominal segment about one and 

 a half times as broad as long and with two transverse rows of dorsal setae com- 

 posed of seven setae to the row; eighth abdominal segment shaped similarly to 

 the seventh but smaller, with transversely striated band. Anterior legs extend- 

 ing beyond the head by the full length of the tarsi and by about one-fourth the 

 length of the tibiae; claws slightly longer and less curved than those on the other 

 legs. Length when much extended, 0.82 mm.; width, 0.10 mm. 



Type Cat. No. 24,586 U. S. N. M.' 



Description based on the type specimen, a female taken from 

 a decaying mass of organic matter at Takoma Park, Maryland. 

 This species is common at Takoma Park, but because of its small 

 size is easily overlooked. 



Microentomon, n. gen. 



Differing from previously described genera of Acerentomidae in having but 

 a single transverse row of dorsal setae to each abdominal tergum. Tergal 

 plates very poorly developed; tergal apodemes broadly rounded and not 

 thickened near their middle. 



Type. Microentomon minutum Ewing. 



In this genus also should be placed the Acerentulus per- 

 pusillus of Berlese, described from Italy in 1910. Berlese's 

 species is said by him to be rare, and he possessed but a single 

 example. The members of this genus are exceedingly small. 

 When well extended they are about .5 mm. in length, but in a 



