LYMNZIDZ OF NORTH AMERICA. 389 
globose form described as L. pinguis by Say, and seems, in many 
cases, to run very close to that of L. ampla Migh. The Pine Lake 
examples have usually a very thick, solid opaque shell, and a large 
proportion are more or less distorted, the most common effect of their 
unfavorable environment being apparently to induce a very abrupt 
and rapid expansion of. the outer lip, which, in most cases, 1s ac- 
companied by a heavy callus deposit all around the aperture.” 
The thick opaque texture is characteristic of many of the species 
from the northern part of the lower peninsula of Michigan. 
REMARKS: Catascopium is frequently confounded with palustris 
and emarginata. It differs from the latter in the manner in which the 
inner lip is appressed to the axis, and in having generally a narrower, 
more fusiform shell and a more elongated aperture. Emarginata is 
typically umbilicated and the inner lip is widened out to form a broad 
expansion, quite different from the narrow inner lip of typical cat- 
ascopium. It differs from palustris in its shorter, wider and less acute 
spire, in having one whorl less and in having generally a wider, more 
fusiform shell and finer sculpture. The columellar plait is not gen- 
erally as pronounced in catascopium as it is in typical palustris. Cat- 
ascopium is, also, seldom malleated while palustris is frequently so 
marked. The more fusiform shape, wider shell, one less whorl and 
the less acute spire will serve to distinguish the majority of specimens 
of catascopium from palustris. It generally has a thicker shell than 
that of palustris. 
Dr. James Lewis' has advanced some suggestive theories in re- 
gard to the relationship of catascopium to elodes (=palustris). Dr. 
Lewis believed that ‘““An equitable temperature, a moderate supply of 
food, limited supply of air, and frequent disturbances of the station 
of the animal by currents in the water, determines the form we call 
catascopium’”’ while “a warmer station, abundance of food, unlimited 
access to the atmosphere, and quite stagnant water, favor the develop- 
ment called elodes.” While this statement is true to a certain extent 
as regards the habitat of the two species, yet the writer has seen no 
evidences bearing out the theory advanced by Dr. Lewis that the eggs 
of catascopium will produce palustris when transferred to a different 
‘environment. The shell may be (and does) become somewhat 
elongated and simulate the palustris form, but it is still catascopium, 
as may be proven by examining the teeth and genitalia. The nearest 
approach seen by the author of catascopium to palustris is in a lot 
of shells from the north end of Owasco Lake, Cayuga Co., New York, 
1Amer. Journ. Sci., IV, p. 4; VI, p. 85. 
