1876.] Cooper’s Helix in Colorado. 531 
with them that one can scarcely walk without crushing several at 
every step. Where they occur so numerously the shells are in- 
variably empty and bleached, and in all probability they have 
been lying in this condition for years. Through burned forests 
where every tree has been charred, and the underbrush entirely 
destroyed, they are to be seen, lying on the blackened ground, in 
even greater quantities than under any other condition. And 
this I accounted for in the following manner: At certain times 
of the year the animals bury themselves in the moist earth, and 
when the forests are fired by the Indians, the heat causes them 
to come to the surface, where they are destroyed, and their cal- 
careous coverings rendered so brittle that they can be crumbled 
into an impalpable dust between the thumb and fingers. 
Different specimens of H. Cooperi often present such a great 
variety of forms that the collector may frequently become con- 
fused in seeking to determine them. Sometimes the spire is ex- 
ceedingly depressed, when the specimen may be mistaken for 
Helix strigosa, while many others are highly elevated and re- 
semble closely large specimens of Helix Idahoensis. Near the 
Grand River, just above its confluence with Piney Creek, I 
MEA picked up a reversed specimen, which, 
among this species, is extremely rare. 
It must be considered as nothing less 
as than a montrosity, yet is exceedingly 
(Fis. 42.) REVERSED specr- interesting in showing to what extreme 
MIN OP HELIX COOPER variation the H. Cooperi is subject. 
As we advanced southward we found the representatives of 
this species decreasing in number and size, until, in the south- 
West portion of Colorado, they are found only occasionally in the 
defiles of the Sierra La Plata. The higher elevations seem to 
be more favorable for the full development of mollusks, being a 
| limestone country, while among the lower sandstones land shells 
Ate almost unknown. We find, then, that there are certain con- 
ditions of climate, elevation, and locality, which are favorable to 
the Satisfactory growth of the hardy and prolific H. Cooperi. It 
ms to thrive better in a temperate than in a torrid climate. 
It Increases more rapidly in numbers, and even in size, in the 
Medium or higher altitudes. It prefers cool, damp, shaded spots, 
_ itm or dry locations. It appears to be confined to the Pa- 
cific slope of the Rocky Mountains; for, if it exists at all on the 
rn side, it is only met with in reduced numbers. 
