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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



on each side of the segments from three to seven. Figure 9 A shows 

 the normal form of these sclerites. Modifications are chiefly in size, 

 distinctness of the sutures, and vestiture. Xenodusa has the para- 

 tergites modified to form the hairy lobes or trichomes (fig. 27 B) 

 which project over the succeeding segment. 



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Fig. 27. — Details of the structure of the abdomen, and the intrafamily 

 variation in the pattern of the intersegmental membranes. 



A, ventral aspect of abdomen of Gastrolohium bicolor (Grav.). B, paratergites 

 and trichome of Xenodusa sharpi Wasm. C, pattern of intersegmental membrane 

 of Lathrotropis jacobina (Lee). D, paratergite of Geodromicus brnnncus (Say). 

 E, pattern of Pacdcrus lactus Er. F, group of setae from sternite of BoHtobius 

 cinctns (Grav.) ; G, pattern of Xantholinus picipcnnis Lee. H, pattern of Stenus 

 scidptilis Csy. I, posterior margin of sixth tergite of Acylophorns flavicollis 

 Sachse. J, pattern of Osorins mundiis Shp. 



The membranes between these intermediate segments are usually 

 marked in a definite pattern with minute spots of regular shape and 

 deeper color. They appear to be actual sclerotizations in the membrane. 

 These patterns are fairly constant in the various groups. The most 

 frequent pattern is one of small rectangular areas arranged either 

 in transverse or in longitudinal rows or both, often changing from 



