OF WASHINGTON. 403 



of themselves justify either wide systematic separation, nor, on 

 the other hand, do they supply evidence of close affinity. There 

 appear, in other words, to have been many independent aberra 

 tions of the normal pore-formula of the twenty-segmented Diplo- 

 poda, and as these variations have probably not been encouraged 

 by selection and have had little or no bearing upon other aspects 

 of the evolution of the group, there is little reason to expect that 

 it will be possible to utilize the pore-formulas as primary char 

 acters in the presentation of a phylogenetic classification of the 

 order Merocheta. 



DUOPORUS, new genus. 



Type : Duoporus barretti, 



Distribution : Mexico. 



Body small; about seven times as long as broad; broadest in front; 

 gradually narrowed caudad. 



Antennae slender, distinctly clavate ; joints in order on length, 6, 2, 3, 5, 

 4, i, 7. Joints 3 to 5 subequal, but distinctly smaller than 6 and 2, which 

 are also nearly equal in length, but 6 is much broader and slightly longer 

 Olfactory cones four. 



Vertex smooth, strongly convex, the suture distinct, but the sulcus 

 wanting. 



First segment semi-elliptic; broader than the head, slightly narrower 

 than the second segment; slightly emarginate in the middle behind, and 

 with a fine raised rim on the anterior and lateral margins; corners not 

 produced. 



Segments dorsally rather strongly and evenly convex, the surface 

 smooth and shining, not marked by a transverse sulcus or depression. 



Lateral carinse moderately broad, about one-fourth as wide as the body 

 cavity, inserted near the middle of the side ; broader on anterior segments. 

 On all segments behind the second the carinae are more or less falcate, 

 that is, emarginate on the posterior margin, and with the posterior corner 

 sharply produced caudad; this feature is much more pronounced on pos 

 terior segments, the carinae of which are narrow and sharplv spiniform. 

 With the exception of a very minute notch near the rounded anterior 

 corner, the margin is entire, thin, and with a very fine raised rim. 



Repugnatorial pores present only on segment 5, the aperture minute 

 and without a raised rim; located in a distinct depression just inside the 

 unmodified raised margin of the carina. 



Supplementary margin very short, concealed under the posterior mar 

 gin of the segment. 



Last segment longer than the preceding, subtriangular in outline, with 

 apex abruptly narrowed and truncate; setiferous tubercles minute. 



Anal valves smooth, margin slightly prominent, setiferous tubercles 

 minute. 



