66 NEOTROPICAL PSELAPHIDAE 



We must be very cautious in using those structural features which may be 

 secondary adjustments, such as the reduction of mouth-parts for a specialized 

 diet, as in the Clavigerinae; or the reduction or loss of eyes and wings in one 

 or both sexes. It is quite possible that a genus may be primitive in its general 

 anatomy, but will have certain parts highly specialized. Thus Rhinoscepsis is 

 a primitive genus in many respects, but there is a reduction in eyes and wings. 

 Species living habitually in deep soil, caves, or the nests of ants and termites 

 are usually illustrations of this idea. 



Key to the Genera 



Prostemum with a median longitudinal carina (lateral straight or 

 oblique carinae may or may not be present separating the pro- 

 sternum from the pronotum, but these are not involved ; where the 

 prostemum is medianly carinate, the carina extends from a point 

 between the bases of the anterior coxae, across the sternum, ending 



at or near the anterior margin) 2 



Prostemum with no median longitudinal carina 6 



2(1). Base of each elytron with four foveae (the basal foveae lie in 

 a line between the suture and the humeral angle ; these basal 

 foveae do not include a subhumeral fovea which may or may 

 not be present just posterior of the humerus and on the flank 



of the elytron) 3 



Base of each elytron with fewer than four foveae 4 



3 ( 2 ). Ventral surface of head with a fine, median carina 



PTERACMES 



Ventral surface of head with a median sulcus 



PTEROPLECTUS 



4 ( 2 ) . Second tergite armed, a prominent tubercle on each side, in the 



male (female unknown) FARONOMA 



Second tergite not armed or laterally tuberculate in either sex 5 



5 ( 4 ) . Disc of pronotum simple, with no central fovea or foveoid de- 



pression BIBLOMIMUS 



Disc of pronotum with a central depression which varies from 

 a small fovea to an elongate, fusiform, longitudinal foveoid 



area THESIUM 



6(1). Base of each elytron with four foveae 7 



Base of each elytron with fewer than four foveae 10 



7 ( 6 ) . Sides of pronotum with one or more distinct teeth^ 8 



Sides of pronotum not dentate^ 39 



* The presence or absence of teeth must be clearly understood. There are three basic 

 types of lateral pronotal margins involved in the Euplectini: entire, in which the margin 

 is a simple line; crenulate, in which the margin is thrown into a series of waves or undu- 

 lations, the period of the wave varying with the species, but the waves being continuous, 

 not discrete entities; dentate, in which the margin is periodically erected into discrete ele- 

 vations. These elevations are nearly always prominent, acute teeth or spines, with sharp- 



