66 
half gradually expanding; aperture obliquely rounded; peris- 
tome simple, thin, incomplete. A thin callus occasionally 
present between the terminations of the peristome; umbilicus 
very large, round, showing all the volutions. 
G.D. 22 L.D. 20 H. 10 
Locality. Marl beds, McKay lake. 
This form is readily distinguished from all others likely to 
be encountered. From Polygyra albolabris it varies in having a 
simple, non-reflected peristome and a large, wide-open umbilicus. 
Living individuals of this species have brilliant red colour 
markings, especially on the upper surface. These, however, 
have mostly disappeared in the fossil specimens. 
Helicodiscus Uneatus Say 
Plate VI, figures 9a-9c 
Shell small, thin, flat, discoidal, surface covered by oblique 
growth lines and numerous fine parallel revolving lines ; periphery 
rounded, sutures deep; whorls four to four and a half, rounded, 
not increasing in size; spire flat, on same plane as the whorls. 
Aperture small, oblique, outer lip bearing several small conical 
teeth; peristome thin, sharp, terminations connected by a thin 
callus, umbilicus large in proportion to the shell, showing all 
the volutions and also the oblique lines of growth. 
G.D. 3-00 L.D. 2-85 H. 1-25 
Locality. Colton lake; also from marl beds, McKay lake, 
fragments only. 
This very small land shell is readily recognized by the 
pronounced parallel revolving lines upon its surface as well as 
by its very large umbilicus, which show the volutions so dis- 
tinctly. Fragments are often found, but the complete shell is 
not common. 
Succinea ovalis Say 
Plate VI, figures 8a-8b 
Shell thin, very fragile, obliquely ovate. Surface covered 
by fairly coarse lines of growth. Whorls three, rapidly expand- 
ing, expecially the last; spire short, sutures fairly deep; aperture 
