TAXONOMIC MORPHOLOGY 25 



The distribution is diverse. Cervical foveae may occur on the ventral face 

 of the cervicum or neck, where they may mark the posterior area of the gular 

 sclerite (Euplectus interruptus) ; or on the dorsal face of the cervicum (Melba) 

 where they form a part of the metatentoria of that region. 



The prostemum with its ankylosed sidepieces usually presents from one to 

 five foveae, following the general plan of the sutural zones of the insect pro- 

 sternal area. The more numerous and well-developed the foveae, the more 

 primitive the species, other things being equal, and conversely, with the final 

 disappearance of foveae, leaving an apparently unmodified sheet of integument, 

 the more highly evolved the species. Such a generalized hypothesis must be care- 

 fully analyzed in the future to prove or disprove its worth. However, the general 

 idea of (1) developed sclerites, bounded by clean sutures, (2) sclerites becoming 

 consolidated, the sutures vestigial and their more resistant intersections or areas 

 persisting as foveae, and (3) eventual disappearance of foveae, leaving a solid 

 chitinous piece, may serve as a working plan. Obviously not all foveae are to 

 be viewed in the light of this idea, e.g. the elytral foveae and pronotal foveae 

 may have their origin too far removed in evolution to be considered. The fusion 

 of the pronotal sclerites into one pronotal piece is an ancient combination in 

 beetles, and the elytra or wing cases are also greatly modified from the meso- 

 thoracic functional wings of other insect stock. The sternal areas, however, offer 

 a promising field, especially when they can be compared with staphylinid areas, 

 admirably reviewed by Blackwelder (1936), whose comparative treatment of 

 the anatomy of the Staphylinidae should serve as a guide in future revisions 

 of the family. 



The pselaphid prostemum consists of two sclerotic areas, which are some- 

 times primitively well defined, and at times fused into one piece. When both are 

 developed, the prostemum has two sclerites. The first is the basisternum and 

 is an anterior piece being bounded by the anterior foramen of prothorax into 

 which the head is inserted, anteriorly; laterally by the notostemal sutures of 

 each side ; posteriorly by the anterior coxal cavities in part and in part by the 

 second sclerite, the furcasternum. The jurcasternum is variously developed and 

 may be clearly visible under the anterior coxae, or virtually absent externally. 

 This last sclerite or division is chiefly concerned in the endoskeletal invagina- 

 tions, the diverging arms of which are anchored in the basal furcasternal area. 



Returning to the prostemal foveae, we find that these are distributed as 

 follows: (1) Anterior Prostemal Foveae, one on each antero-lateral angle of 

 the basisternum, usually invaginated in the notostemal suture when it is clearly 

 formed. (2) Lateral Prostemal Foveae, one on each postero-lateral angle of 

 the basisternum, usually invaginated in the area where the notostemal suture 

 anastomoses with the stemacostal suture, the transverse suture separating the 

 two prostemal areas. However the lateral prostemal foveae may be located 

 far from this point, and lie, one above each coxal cavity in the sternacostal 

 suture, or, if this is not present or not in its normal position, in the posterior 

 margin of the basistemum above each coxa. Thus the lateral prostemal foveae 

 are essentially related to the anterior coxae, and form an anatomical land- 



