68 
rounded; spire acutely conic, sutures deeply impressed; aper- 
ture roundly ovate; outer lip thin, sharp; inner lip reflected 
over the umbilical region leaving a very narrow chink; callus 
on the parietal wall heavy and smooth; shell sometimes nearly 
imperforate. 
H. 18-0 W. 9-0 A.H. 8-0 A.W. 4-1 
Locality . Marl beds, McKay lake. 
This shell is rare and in the marl beds it is almost impos- 
sible to find complete specimens. The fossil form has in many 
cases the spiral ornamentation completely obliterated. Its 
shell is much larger than either of the succeeding species and 
there is no other fossil form in the Ottawa valley which is at 
all similar. A closely related species L. catascopium , which is 
more globose and has the inner lip closely appressed to the 
parietal wall, completely closing the umbilical chink, should be 
looked for in these marl deposits. It has not yet been found 
here as a fossil. 
Lymnaea obrussa decampi Streng 
Plate VII, figures 14a-14f 
Shell small, thick and solid, subconic, growth lines distinct, 
but fine revolving lines absent; whorls five, flattened above 
and convex below, periphery somewhat flattened. Sutures 
deeply impressed; spire short, of about the same length as the 
aperture; aperture long and narrow, rounded below and nar- 
rowed above, forming a shoulder with the parietal wall of the 
previous whorl; inner lip slightly reflected, but not flattened 
against the parietal wall; umbilical chink fairly conspicuous, 
but in some cases nearly covered by the inner lip of the aperture. 
H. 9-75 W. 5-25 A.H. 5-0 A.W. 2-5 
Locality. Marl bed, Colton lake. 
Lymnaea obrussa decampi is a very characteristic species 
of the marl beds at the above locality. It has not been dis- 
covered living in Ontario. In the fossil form its range extends 
from Illinois to New York. This little shell would not be 
readily confused with any except L . gctlbana (See the following 
species). In general, it is less robust and globose than L.galbana , 
