NO. 1256. FOSSIL SHELLS OF THE COLORADO DESERT— STEA RXS. 2 9 1 
form, with ten to fourteen regiilarh'^ occurring rounded undidation.s 
or ribs. HemphilFs Pompholyx codatci^ from near the Dalles of the 
Columbia River, has the same sculpture. 
Another sculptural aspect that is not infrequently met with is what 
has been termed malleated. 
De Ka3'\s P. jMcata^ ''in some specimens," exhibits ''distinct square 
facets." Physa carltoni Lea, from near Antioch, at the junction of 
the Sacramento and San Joaquin rivers, is sometimes malleated. In 
P. malleata Tr3'on we have another illustration. 
All of the various sculptural aspects above described occur also 
in the Limnceidce^ of which the following species may be named: L. 
caj)erata^ L. cataseopiiim^ L. colinneUa, L. decoUata, L. emarginata, L. 
elodes, L. lanceata, L. lepida. L. indtaJliana^ L. pahistris^ L. simiassi., 
L. umhrosa^ and innumerable varieties or races of the above, and in 
Call's fossil L. honnevillensis, from the quaternary of the Great Basin 
and his living Z. {Radix) ampla., var. utahensl.s from Lake Utah. 
It will be observed by reference to the descriptions of the many 
species of Physa herein quoted that no mention of salinity is made in 
connection with the waters in which the shells were found; the same 
remark also applies to the various species of Liiiiiuea above named. 
Regarding the latter we hnd the longitudinal, transverse or spiral 
sculpture, the latter either incised or produced. The malleated aspect, 
etc., in Z. aatpla^ and these in many and various aspects of differen- 
tiation in Limncea einarglnata^ as may ])e seen in the National Museum 
(Cat. Nos. 12388T to 123894, inclusive). 
In the large series from Eagle Lake' in central Minnesota, where 
neither saline or thermal conditions need to be considered, nearly all, 
if not all, of the sculptural characters that occur in the numerous 
species of Physa and Limncea^ above cited, are present, besides such 
features as relate to form and solidity. 
The partially or wholly malleated surface so often met with in the 
Limnceids regardless of altitude or the salinity of the water, and less 
frequently in the Physas^ is explainal)le by the character of the lake 
or pond bed in which these dinted forms occur. The character of the 
bottom, even in a pond of limited size, often exhibits very consider- 
able differences in the matter of compactness or density; alluvial 
mud, clayey mud, clay or sand, with tine or coarse gravel intermixed 
with fragments of aquatic plants and plant stems in varying propor- 
tions. The 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 
impact of the surrounding mattin-. contril)ute to produce the malle- 
ated or dinted surface, which frequentl}' exhibits a somewhat spiral 
arrangement. 
iProc. U. S. Nat. Mus., XXII, No. 1190. 
