204 PLANORBIS. 
18. PLANORBIS TRUNCATUS, Mies. 
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) 
