26 NEOTROPICAL PSELAPHIDAE 



mark in the topography of the prosternum. When they are present, these foveae 

 can be seen to best advantage in potashed slide-mounts in which the coxae have 

 been removed. (3) Median Prostemal Fovea, when present, in the posteriorly 

 angulated portion of the basistemum where it forms a slight projection between 

 the anterior coxae, or invaginated in the sternacostal suture medianly between 

 the coxae. 



It should be noted that all combinations may exist, from one, three to 

 five of the foveae present or absent, and the foveae may be well-formed in- 

 vaginations, deeply conical and with their walls segmentally creased or whorled 

 to foveoid depressions. The primitive Sonoma {Raj onus) tolulae has all five 

 present, and not very well developed; the anterior prosternals especially are 

 weak. Here the sutures are more clearly defined, but in Rhinoscepsis bistriatus 

 only the lateral prostemal foveae are present and these are strongly defined 

 and nude, and in Euplectus (Pycnoplectus) interruptus only the lateral pro- 

 sternals are present and these are pubescent. The figures and descriptions will 

 give other data on these foveae, and we should remember that this classification 

 of foveae is a tentative one upon which a complete picture may be erected 

 for the family as a whole. 



Because the foveal system is being elaborated here as a taxonomic aid, 

 rather than as a detailed account of comparative anatomy, the foveae of the 

 meso- and metasterna are considered collectively, inasmuch as the student 

 examining the venter is confronted with a compact region holding the inter- 

 mediate and posterior coxae. In addition to certain rare or aberrantly placed 

 foveae, the meso- and metastemal field presents a varying number of foveae, 

 from one to eleven, which may be considered here. 



I. Prepectoid Foveae. These are invaginations on the prepectoid area, 

 and are very rare. When they are present {Sonoma {Raj onus) tolulae) they 

 lie in a region which would be traversed by the stemopleural suture if it were 

 present, and appear as the most anterior pair of foveae. The prepectoid abounds 

 in complicated depressions; and foveoid depressions are suggested by the 

 topography of Euplectus {Pycnoplectus) interruptus and Adranes lecontei, to 

 name two extremes; true prepectoid foveae are known, however, only in 

 tolulae, among the species studied thus far. Their presence is regarded as a 

 primitive feature, since the prepectus apparently lost its identity, as a discrete 

 element, among pselaphids by fusing more or less with the sternum and epister- 

 num of the mesothorax. 



II. Lateral Mesosternal Foveae. These are a pair of foveae which ap- 

 pear as invaginations of the sclerotized posterior wall of the prepectoid and 

 also in the region of the stemopleural suture when it is present. They are prac- 

 tically never absent, being the most constant of all the stemal foveae, and 

 traverse the prepectoid wall where it is elevated above the mesosternum. They 

 course medianly, and their apertures are usually difficult to locate in dry 

 triangle mounts because of pubescence in some groups (Ctenistini, Pselaphini, 

 Tmesiphoms, et cetera). In slide mounts, however, under high magnification, 

 they are quickly discerned. 



