las. In Arizona some of these slides are half a mile in length. 
Then we dig, endeavoring to find a situation that the snails like 
the best. They leave a white ring the size of the aperture upon 
the stone where they have rested over for sleep or hibernation. 
One soon can tell whether these tracks are fresh or not. They 
may be found next to the soil a couple of feet down, at other times 
around the edges of the slide near their feeding grounds. Some 
times a pestilence seems to have swept through the rocks leaving 
dead shells behind, but most always live sheils can be found in 
the rock pile somewhere. 
Like other groups the different species have different habits. 
We found S. rinconensis attached to large blocks of granite in 
the opening. To pull them broke the edges of the apertures, so 
we pounded the rocks with a hatchet to jar them off. 
S. coloradoensis is found under sing!e stones next to the soil. 
An unnamed species was found under logs in the heavy timber. 
Usually the north slipe of the mountain, in rock slides with izoose- 
berries and rose bushes, is the best place, but quite often they 
are found on the hot side of the mountain, in rock piles without 
shade. Several times we have dug for two hours without finding 
a live one. If the weather or seasons make any difference in the 
harvest we have not found it out. Coloradoensis move about the 
leaves and grass during wet weather, but a Sonorella is usually 
found at home, whether under snow or in the hot sun of a summer 
day. Once I found a Sonorella at the top of a slide in the dirt 
packed into the slide by cattle. Another time I dug among the 
stone at the side of the slide over which a heavy sod had grown, 
and in both cases got a good collection of live ones. 
This so-called porphyry and quartzite is the best for Sonor- 
ellas, but they are also found in lime and all kinds of granite. A 
dark stone with didcoloring chemicals is usually poor picking. 
Sandstone is also suitable for Sonorellas. 
21:0036 Sonorella baileyi orcutti Bartsch. 2487. 
In May, 1917, I had the pleasure of revisiting the old historic 
stage station known as Mountain Springs, on the eastern edge of 
San Diego county, California. Aside from cacti, Yuccas, Nolinas, 
Aizaves. and a few other distinctive desert plants, there is no vege- 
tation on the steep eastern declivity of the mountains at this 
point. It was here, under granite rocks, that years ago I found 
dead shells of what Dr. R. E. C. Stearns decided was Helix colo- 
radoensis, then but recently described. (See M. 1634, 2660, 
2487). I was the guest of Mr. H. N. Lowe, and together we tried, 
in vain, to unearth a live specimen of this still imperfectly known 
snail. It seemed to be a most discouraging locality for snail life, 
but I suspect that we were both too timid about going deep. A 
few dead shells only rewarded our search. I suspect it will not 
prove to be a Sonorella when found alive, tho its environment 
would encourage the belief that it is genuine. As I understand, 
there are no distinguishing characters by which the shells of 
Sonorella and Epiphragmophora can be positively separated. 
At the suggestion of Mr. Lowe, I asked Mr. Ferriss for a short 
account of how to find Sonorellas, with the pleasing result above 
(see 21:35), and hope some future naturalist will have the per- 
sistence to find some at home among the Californian hills. 
21:0037 Walker, Bryant: method of evolution in Unionidae. 
Occasional papers of the museum of zoology, Univ. of Mich. No. 
45. From the author. 
