NO. i-2o(;. FOSSIL SHELLS OF THE COLORADO DESERT— STE A RNS. 275 
dicular section exhibited in the well at Walter's station on the South- 
ern Paoitie Railroad, as noticed by me in 1879 \ This well was sunk 
to the depth of 45 or 47 feet when water was struck. The section 
showed a fine claj'ey sediment such as is precipitated from turbid 
waters in a sluggish or placid condition; this sedimentary deposit con- 
tained throughout examples of Paliidestrina and Physas, or fragments 
of l)oth. 
At many places in the desert occur what are known as "dry bogs." 
These are the dried up pools of former j^ears; they are a most danger- 
ous menace to the unwary traveler; the vegetation which the waters 
of these former ])asins supported, when dried, is sufficiently strong to 
support the coating of drifted sand by which they are disguised; the 
weight of man or beast is sufficient to break through this thin crust 
and submersion is inevitable. Some idea of the number, extent, and 
character as well as of the apppearance of the desert at the time when 
these bogs were pools or lagoons, may be seen at a glance in the local- 
ity known as Flowing Springs, 40 miles west of Yuma, where many 
of these so-called springs have the area of ponds or lakelets of consider- 
able size and support a luxuriant aquatic vegetation. Here also may 
be seen thousands of birds of various species, swimmers, waders, etc., 
as well as land birds, and the part feathered tribes have performed in 
the distribution of these little conferva inhabiting moUusks is forcibly 
suggested. 
THE PALUDESTRIN.^. 
The forms under consideration were collected b}" the writer in 1882, 
in the immediate neighborhood of various stations along the line of 
the Southern Pacific Railroad in the Colorado desert of California. 
Favorable circumstances afforded considerable time at each of the 
places stopped at, so that a large number, man}" thousands, of the few 
species that are so abundant on the surface of the desert were obtained. 
The shells specially reviewed belonging to the genera Paludextrina 
and PJu/m, inhabit springs, pools, and the shallow, marshy borders 
of ponds and lakes; they appear to prefer quiet waters rather than 
flowing brooks or larger streams. Though classed as fresh-water 
species, they are not infrequently found in waters that are alkaline or 
saline, also in springs of a temperature as high as 100° F. The par- 
ticular species of Paludestrlna mentioned has heretofore been vari 
ously referred to the genera Amnicola, Ifelania, HydTobia^ and later 
to Stimpson's genus Trymiia;^ still later to Bythinella. It has been 
' Remarks on iossil shells from the Colorado Desert, in the American Naturalist, 
March, 1879 (read before the California Academy of Sciences). 
^For Stimpson's figure of the type of Tryonia, see fig. 29, and pp. 48 and 49 of 
Researches upon the Hydrohiinse, etc., Smithsonian Miscellaneous Collection No. 
201, August, 1865. Binney's figure in Land and Fresh Water Shells of North America, 
p. 71, Part III, Smithsonian Miscellaneous Collections, September, 1865, does not 
represent it. 
