24 NEOTROPICAL PSELAPHIDAE 



can be isolated on this character. Tyrini also show considerable variation, but 

 as a tribe come under this first group, while Euplectini have these coxae approxi- 

 mate or contiguous. 



The chitinous invaginations of the integument — the endoskeleton — are well 

 formed in pselaphids. We have previously noted the supratentorium of the 

 cephalic capsule, its intimate relationship with the vertexal foveae, and with 

 the gular fovea. The author has been at some pains to check the condition cited, 

 and this study has covered well over a hundred nearctic and neotropical species. 

 Earlier, Stickney (1923) recorded the supratentorial details for Pilopius 

 lacustris and Fustiger fuchsi. 



The endoskeleton of pro-, meso-, and metathorax is less well understood. 

 The prosternum has a one-piece prosternal furoa of the U-type which extends 

 internally from the dorsal wall of the coxal cavities, one arm of the furca from 

 each cavity and the two arms broadly joined at their bases. The mesosternal 

 furca is composed of two discrete arms, one extending internally and anteriorly 

 from the dorsal wall of each coxal cavity. The metasternal furca if of the 

 Y-type, with a basal stem invaginating in the center of the posterior metasternal 

 field, and this basal piece bifurcating, with the arms extending dorsad into the 

 thoracic haemolumen and musculature. 



Chitinous invaginations of the abdomen, associated with the spiracles, are 

 present in genera investigated, and are notable in certain Euphalepsus. From 

 certain points of view the sclerotized male copulatory apparatus could be con- 

 sidered invaginations, in view of their relation to the ninth and tenth abdominal 

 segments, but this is not involved in the endoskeleton. 



Another general morphological subject to be examined here is the foveal 

 system of Pselaphidae. The integument is diversely and richly supplied with 

 small integumental invaginations. Possibly no other single feature is of such 

 use in the identification of genera and species as the foveae — their presence or 

 absence, number, type and distribution. The vertexal and gular foveae have 

 been previously discussed, and are only a few of the many foveae present. The 

 significance of foveae in Pselaphidae has been underestimated, and at least 

 two aspects need emphasis. 



In the first place foveae often suggest a general sensory function. The rich 

 pubescence of many foveae lends credence to this hypothesis but careful experi- 

 ments are necessary before definite ideas can be held on this point. 



In the second place, the morphology of foveae is easily studied by slide- 

 mount technique and a considerable amount of data are at hand for their 

 evaluation (cf. especially Plate V). The topographic position of many foveae 

 in Pselaphidae tends to indicate that they have arisen where sutures coalesce. 

 Therefore their presence is an indirect argument for the structural consolidation 

 of the body, so well shown in pselaphids, and so conspicuous by its absence in 

 the staphylinids. When a fovea is examined, it is seen to be a thimble-shaped 

 or cylindrical invagination of the hardened integument. Its walls are usually 

 either segmentally creased, or spirally whorled. Usually it is short and conical; 

 in other cases its lumen is long, tubular and sinuate. 



