22 NEOTROPICAL PSELAPHIDAE 



Pilo-pius). The normal ctenistine scale is gradually broadened distally, and its 

 integumentary puncture is provided with a tubular extension into the chitin. 

 The Arhytodini and Hybocephalini also have squamous pubescence in part. 



The setae may be normally inserted, or may be lodged on small asperities 

 (as on the antennal cones of Tychus), or may be placed upon relatively large 

 tubercles (asperate setae on the distal antennal face of Rybaxis clavata) . These 

 antennal cones are present in many of the Pselaphidae examined from various 

 parts of the world, and under oil at high magnification they can be differentiated 

 from the normal antennal setae. When we have more data concerning the an- 

 tennal cones, they may serve as a taxonomic aid (Park, 1935c), as has been 

 noted for the male genitalia previously. For examination of these cones see the 

 distal antennal segment of Melba, Dalmosella, Euplectus, Bibloplectus, Tychus, 

 Pilopiits, Rybaxis and Tmesiphorus among Illinois genera; Central American 

 species examined {Hamotus turalbus) have the antennal cones well developed. 

 In this species the cones are normally transparent and very difficult to see in 

 unstained preparations but appear to be articulated upon rounded asperities; 

 normal antennal setae are usually quite distinct and are smaller than cones and 

 placed in slightly recessed punctures. These cones may be homologous to the 

 distal setiform cone of the last segment of the pselaphid maxillary palpus; at 

 least they appear similarly under magnifications of 1000 diameters, and like 

 the palpal cone, may be sensory in function. It is interesting to note that such 

 cones are also developed upon the antennae of Thysanoptera, Chalcididae, 

 Proctotrupidae, et cetera. 



The ventral face of the head may bear knobbed or capitulate setae [Melba, 

 Trimiomelba, Eupsenina) in a definite pattern; in some genera (Thesiastes) 

 these capitulates are few in number, strongly knobbed, and more or less spino- 

 form; in Bibloplectus these setae are truly spinoform processes of the integu- 

 ment. On the other hand the setae on the ventral surface of the head of Rhex- 

 idius are very long, very abundant, and only slightly capitulate, e.g. the setal 

 tips are gradual elongate-oval swellings, sometimes absent entirely; in Euplec- 

 tus, the same area bears sparse, recurved, noncapitate setae. 



An extreme in the modification of the setal tip is seen in the maxillary palpi 

 of certain species, for example Pilopius lacustris, where the setae of the distal 

 segment are long, uniformly slender to the apex which flairs into a thin, flat plate 

 at right angles to the shaft. These setae may be termed umbrella-setae. Also 

 the distal palpal segment of Ephimia and Juxtahamotopsis have peculiar setae: 

 short, thick, rigid, blunted, translucent, and appear to be small spikes. In this 

 case we may have a transitional stage from seta to palpal cone. 



Almost always one seta arises from a single puncture, but in Adranes the 

 setae of the head, pronotum and elytra appear to be doubled, that is, two di- 

 vergent setae arising from a single puncture. This is not true, species of Adranes 

 following the general rule, and under high magnification each seta is seen to 

 bifurcate a short distance beyond the puncture, to give two long processes. 



The remaining features of this comparative review deal with the sternal 

 areas, the endoskeleton, and the sternal foveae. The Pselaphidae have the pros- 



