170 NEOTROPICAL PSEL APHID AE 



united, with outer basal angle forming a tooth which projects pos- 

 teriorly to slightly overlap the tenth segment; this eleventh segment 

 remarkable for the extent of excavation, the entire surface is exca- 

 vated save for an elongate area at mesial apical face; 1.2 mm. long; 

 Vera Cruz, Ver., Mexico inflatus 



Antennal segment XI with a transverse excavation which occupies 



much less than the basal half of segment 6 



6. Antennal segment XI with a distinct subbasal tooth; known from 

 Yucatan denticornis 



Antennal segment XI with no tooth, but with the basal margin of 

 excavation sharply defined and provided with a long, dense tuft of 

 inwardly directed setae on the inner basal angle; 1.0 mm. long; 

 known from British Honduras ventricosus 



Group V New Group 



This new group has been erected for a remarkable new species of the 

 Panama Canal Zone. The key character given for the separation of this species, 

 undedmtympus, is simply a convenient structural feature for rapid separation 

 from the other species in Group IV, and does not by any means indicate the 

 divergence between these two groups. This Panamanian species has the male 

 second tarsomere of the anterior tarsi swollen, flattened below, and provided 

 with a brush of setae, as in the males of Xybaris, Achillia, Bryaxina, Braxyda. 

 This secondary sexual character is not common to Scalenarthrus, and it is pos- 

 sible that the new species belongs in a separate subgenus or even a new genus. 

 It is of interest in this precise connection to point out the parallel in another 

 subglobose, related genus Cryptorhinula, where the anterior tarsi of the males 

 are not dilated save in oedipus (Sharp) , where the second tarsomere is peculiarly 

 swollen. 



In the essential key characters undecimtypus is Scalenarthrus, with affini- 

 ties with Pselaptus and Xybaris. Numerous peculiarities will be found in the 

 description which follows, especially the male antennal club and the remark- 

 able air-filled tube on each side of the head. 



Scalenarthrus undedmtympus new species 



Holotype Male. Measurements: Head 0.20 x 0.26 mm.; antennae 0.335 

 mm.; pronotum 0.23 x 0.30 mm.; elytra 0.40 x 0.47 mm.; abdomen 0.13 x 0.40 

 mm.; total length 1.00 mm.; greatest width 0.47 mm. (PL VII, 2, 3, 12) 



Body subglobular, light yellowish-brown, moderately shining, very lightly 

 punctulate; pubescence rather short (0.01 mm. on pronotum and 0.022 mm. on 

 elytra) , inconspicuous save under high magnification but rather abundant. Head 

 subquadrate from a dorsal view, with prominent eyes. Eyes with about twenty- 

 four coarse facets, relatively long (0.09 mm.), more than twice as long as the 

 convergent tempora which are short (0.04 mm.). Vertex flattened, higher than 



