62 NORTH AMERICAN BLATTIDAE 



the median vein; ulnar vein wealcly curved with a number (3 to 

 7) of proximal incomplete rami and a number (4 to 6) of moderately 

 arcuate distal rami extending to the distal margin of the wing; 

 intercalated triangle small and inconspicuous. ^^ Males with 

 median segment not specialized, but with sixth and seventh dorsal 

 abdominal segments greatly specialized. Sixth segment emar- 

 ginate mesad to near its proximal margin, with sides of emar- 

 gination convex, bearing beneath on each side near the apex 

 of the emargination a minute chitinous projection, armed dorso- 

 distad with closely set delicate microscopic teeth which are directed 

 cephalad (PI. II, fig. 12); seventh dorsal abdominal segment in 

 greater part lying under sixth segment, but with a narrow, medio- 

 longitudinal, decidedly elevated ridge lying between the armed 

 projections of the sixth segment. Eighth dorsal abdominal seg- 

 ment unspecialized. Cephalic femora with ventro-cephalic mar- 

 gin armed with (usually about four) heavy, elongate, well sep- 

 arated, proximal spines, succeeded distad by a row of minute, 

 closely set, piliform spines, which is terminated distad by three 

 heavy, elongate (in increasing ratio) spines. Other ventral mar- 

 gins of femora supplied with widely spaced, heavy, elongate spines. 

 Tarsi elongate; a single, small, rounded pulvillus present distad 

 on each of the four proximal tarsal joints. Small arolia present. 



The Vilis Group of the Genus Ischnoptera 



This group includes probably the only native North American*^ 

 species of the genus Ischnoptera. It precedes and is separated 

 from the IMorio and Rufa Groups by features of the male supra- 

 anal plate, which is of generally similar trapeziform shape but chitin- 

 ous throughout, while the females of the two species known to us, 

 vilis and deropeltiformis, both have greatly reduced tegmina. The 

 general coloration in these two species is very dark, the pronotal 

 sulci in the males is pronounced, the male subgenital plate is of 

 the general type found in the Morio and Rufa Groups. 



82 In females of the Morio Group these features are absent, due to great rcchiction in 

 the organs of flight. 



'*3 We here use North America in the restricted sense, taking the continent north of 

 the Mexican bounthiry as covered in the present jjajjer. 



