
4 THE CHICAGO ACADEMY OF SCIENCES. 
tions. ‘he habits of these mollusks include, if not properly speaking 
burrowing, wallowing or submersion, and moving as they do with 
somewhat of a rotating motion, this, combined with the moderate 1m- 
pact of the surrounding matter, contributes to produce the malleated 
or dinted surface, which frequently exhibits a somewhat spiral arrange- 
ment.” 
The writer believes that Dr. Stearn’s theory is correct, as it 1s 
borne out by the ecological study of such species as palustris, reflexa 
and bulimoides techella. These species, with some of their varieties, 
are inhabitants of ponds and streams which dry up during a part of 
the year, compelling the animal to burrow in cracks, crawfish holes 
and under debris of various kinds. The newly formed shell is fre- 
quently added while the animal is wallowing in a few inches of water 
and thus takes the form of the surface upon which it is resting, which 
is usually very uneven. It is a significant fact that a malleated. shell 
taken from the environment of a summer dry pond and placed under 
uniform conditions in an aquarium where there is an abundance of 
water, continues its shell growth without a trace of malleation. It is 
also noticeable that the malleated individual lives in more or less shallow 
ponds and pools among all sorts of debris, while those individuals 
without malleation and with smooth shells live in deeper waters of a 
less transient nature. Lymnzas from rivers and large lakes are seldom 
malleated, as may be seen in most individuals of catascopium and stag- 
nalis. Dr. James Lewis believed that malleation was due to a rapid 
growth in warm water, which caused the shell to solidify unevenly.’ 
Dr. Lewis seems to have laid great stress on the temperature of the 
water, instead of on the mechanical action of the environment, which 
seems, from present data, to have been the primal cause of this feature. 
Temperature does influence growth in other directions, however, as 
may be seen in almost all species which have a wide northern range. 
2. Spiral sculpture. The presence of spiral, more or less wavy, 
incised grooves has been frequently noted by many observers. This 
sculpture is characteristic of the majority of the species of Lymneide, 
and, in fact, may be called typical. It is developed to a high degree 
in catascopium, the shell of which appears as though engraved with 
a tool. Stagnalis also exhibits the same appearance, although the lines 
are finer. Under the compound microscope these so-called spiral lines 
are seen to be caused by the elevation of the growth lines to form an 
infinite number of small coste which are interrupted more or less regu- 
larly, these breaks between the ends of the coste giving the appearance 
1Am, Jour. Conch. VI, p. 85. 
