204 



PLANORBIS. 



18. PLANORBIS TRUNCATUS, Miles. 



Plate 6, fig. 17, 18, 19. 



Shell suborbicular, color light chestnut ; the 

 right side deeply umbilicated, the concavity 

 bordered by an obtuse carina ; the volutions, 

 seen from this side, are scarcely more than 

 two ; left side truncated, presenting a flat sur- 

 face extending across all the whorls, the 

 suture being marked by an obtuse raised line, 

 which likewise extends around the edge of the 

 truncation ; the space between the volutions 

 of this raised line, as well as the entire body 

 of the shell, is beautifully marked with deli- 

 cate longitudinal lines, which are crossed by 

 the minute, raised, transverse lines of growth ; 

 whorls on the left side four or five ; aperture 

 ovate, widest on the right side, which extends 

 beyond the general plane of that side of the 

 shell ; the lip on the left side is straight for a 

 short distance from the body whorl, and to a 

 (51) 



