EAPO See eee 2 cries tale nee 
NATURAL SCIENCES OF PHILADELPHIA. 89 
9 9.5 9 OS) MN: 
15 14 4k 14.2 mm. 
54 Die yd eee ee 
9.2 9.8 9 8.7 mm. 
14 1305 13 12 4 mm. 
ee oF 54 oF 
In these shells the peripheral angle is about as in Cave Creek types, 
but the base is smoother, 
the  striation nearly 
effaced, and spiral strize 
are wanting or very rarely 
a few may be faintly 
seen under the keel. 
Shells from Stations 
1, 2, 6, 7, 8, 12 agree with 
those from 14. These 
stations are on rather 
steep slopes with gener- 
ally northern exposure, 
and from somewhat 
over 6,000 to about 7,000 
feet elevation. The 
distribution over this 
area is nearly or quite 
continuous. 
At Station 3, just over 
the crest of the ridge, on 
the Pinery Canyon side, 
probably a little over 
7,000 feet elevation, the 
shells are smaller, 11.8 
to 138 mm. diameter; 
otherwise similar. This 
station is very high and 
exposed, on a sunny 
slope, hence extremely 
dry and arid; but the 
following record shows 
that mere elevation is 
not a factor of impor- 
tance. On thesouth side 
of White Tail Creek, only 
Fig. 13.—O. c. obsoleta P.and F. A, White Tail, 
Station 14; B,C, Limestone Mountain. Drawn 
to same scale as figs. 10 and 11. 
