168 NEOTROPICAL PSELAPHIDAE 



2. Antennal segment III subconical, IV-VIII quadrate, IX transverse, 

 X trapezoidal, less transverse than ninth, XI short, ovate; known 



only from Yucatan subcarinatus 



Antennal segment III-VIII moniliform, IX quadrate, X transversely- 

 oblique and triangular and wider internally, XI large, ovate; known 

 only from the Lesser Antilles guadelupensis 



Group II 



First visible sternite between the posterior coxae minutely carinate; 

 frontal sulcus obsolete or quite shallow medianly 2 



First visible sternite between the posterior coxae not at all carinate, 

 but broadly concave ; the transverse frontal sulcus equally deep for 



its entire length concavus 



2. Antennal segment IX briefly obconical, IX ovate-elongate, as long as 

 the preceding four segments united schaufussi 



Antennal segment IX transverse, IX large, ovate, the base very slightly 

 subobliquely truncate (showing an affinity for Group III in this fea- 

 ture), and as long as the five preceding segments united. . . .simplex 



Group III 



Known only from a single species, obliquus, from Guanajuato, Mexico, 

 but fortunately both sexes have been described. Length L2-1.25 mm. The female 

 has the eleventh antennal segment relatively small, as long as the four preceding 

 segments united, and regularly ovate in shape. The male has the last three seg- 

 ments abnormal in shape, and appears to the author to be misplaced in RafTray's 

 key, since the abnormalities of the antennal club would seem to place the group 

 under step "4" of our key, rather than step "2"; however the degree of abnor- 

 mality is much less than in the fourth and fifth groups. The male obliquus has 

 the ninth antennal segment broadly transverse, with the mesial face simply 

 convex and the lateral face narrowly acute at the distal angle; tenth segment 

 very much more transverse and shorter than ninth, with the mesial face convex 

 and the lateral face very narrowly produced and acute ; eleventh antennal seg- 

 ment as long as the preceding five segments united, with a very obliquely trun- 

 cate base, this obliquity following the arc of the distal margin of the tenth seg- 

 ment, and with the external basal angle of the segment very acute, thus the 

 lateral face of the segment is distinctly longer than the subsinuate mesial face. 

 Because of this abnormal club an alternative key to the groups of Scalenarthrus 

 is given which departs still further from the Raffrayan pattern, but may serve 

 to check one's group allocations. 



Group IV 



This the largest group in the genus and holds many remarkable antennal 

 modifications. The following key to males, unless otherwise stated, does not 



