65 
Polygyra albolabris Say- 
Plate VI, figures 6a-6c 
Shell large, fairly solid, depressed globose. Whorls covered 
by fine oblique striae, somewhat more prominent on apical than 
umbilical aspect, revolving lines irregular, very minute; whorls 
five to six, rounded above and below, gradually increasing; 
sutures deeply impressed, periphery rounded, aperture rounded; 
shell constricted just behind the aperture; peristome thick, 
smooth, and reflected, not continuous; lower end of peristome 
reflected over the umbilicus rendering it imperforate. 
G. D. 29 S. D. 23 H. 18 
. This gastropod is much larger than any other in the vicinity 
and can be readily distinguished by its reflected aperture, semi- 
globose shape, and covered umbilicus. 
Polygyra monodon Rackett 
Plate VI, figures lOa-lOd 
Shell small, solid, surface covered with minute growth lines, 
but occasionally almost smooth, convex above and below, 
periphery rounded, sutures deep; whorls five to five and a half, 
slightly flattened on top, broadly rounded below, increasing 
gradually, though slowly, last whorl constricted just back of the 
aperture; spire somewhat elevated; aperture narrow lunate; 
peristome thick, reflected, smooth; thin callus on the parietal 
wall, on which is a long, thin tooth between the terminations of 
the peristome and roughly parallel to its lower edge; umbilicus 
partly open, occasionally imperforate. 
G. D. 10-5 S. D. 9-00 H. 6 
Locality . Marl beds, McKay lake. 
This shell is readily distinguished by the large tooth on the 
parietal wall, narrow aperture, and open umbilicus. 
Pyramidula ( Patula ) alternata Say 
Plate VI, figures 7a-7c 
Shell fairly large, thin shelled, depressed globose; surface 
covered with coarse, oblique lines of growth, periphery sub- 
carinate; sutures deeply impressed; whorls five or five and a 
19856—51 
