70 
thickened within by a callus; thin callus on parietal wall, base 
of shell forming a deep, wide, umbilical depression exhibiting 
all the volutions, 
H. 4-9 W. 8-75 A.H. 4-15 A.W. 3-5 
Locality. Marl beds, McKay lake, and elsewhere through- 
out the Ottawa valley. 
This is a characteristic species from these deposits. It is 
readily recognized by the funnel-shaped depression both above 
and below, and by the V-shaped portion of the aperture which 
rises far above the preceding whorl. It is a widely-distributed 
species at the present day, extending well over North America 
except on the Pacific slope. Many marl specimens show traces 
of former apertures by an irregular transverse thickening of the 
shell at intervals, with a change in direction of the whorl. 
Figure 16e shows one individual in which the whorls increase in 
size with great rapidity. P. antrosus var. striatus with strong 
spiral lines, should be sought in these marl deposits. 
Planorbis campanulatus Say 
Plate VII, figures 17a-17d 
Shell sinistral, discoidal, more or less rounded; surface, 
shiny, with lines of growth oblique, raised, numerous, and 
largely equidistant; whorls four and a half, rounded above and 
below, bu„ occasionally sub-carinated above; whorls increasing 
in size uniformly; spire flat or slightly depressed below the 
general level of the whorls, exhibiting all the volutions ; sutures 
distinct; periphery rounded; base of shell rounded with a deep 
umbilicus showing two volutions; aperture irregularly lunate, 
slightly expanded above, more so below ; mouth of the aperture 
dilated to a great extent forming a bell-shaped expansion; last 
whorl contracts slightly just before commencement of dilation; 
heavy callus ridge beneath constriction forms narrow throat; 
peristome thin, slightly reflected, joined to the parietal wall by 
thin callus; campanulate expansion, rarely showing traces of 
revolving lines and lines of growth which are more irregular 
than on remainder of shell. 
H. 5*2 W. 9*2 A.H. 4-5 A.W. 3*7 
