FRESH-WATER MOLLUSCA OF SAN FRANCISCO 
COUNTY. 
BY J. G. COOPER. 
When residing in San Francisco about twenty years ago, I made 
a list of the species then known to inhabit the county, and consid- 
ering the changes since made in the topography of the country by 
the progress of improvement, it may be interesting in future to com- 
pare the list with what may be found there at later dates. Ina late 
article on the Land Mollusca of the Bay Region I remarked that 
three species had been introduced by human agency, and were be- 
coming naturalized. It is very probable that some fluviatile species 
may be hereafter found in reservoirs and artificial ponds, brought 
from other parts of California by accident, such as adhesion of their 
shells or eggs to the feet of water-birds. As an evidence of such 
occurrence elsewhere I may mention that Mr. W. J. Raymond 
found three species which seem to have been introduced since San 
Jose reservoir was constructed, viz., Nos. I, 4, 10, following, and 
Spherium lenticula Gould, none of which I found in the Los Gatos 
Creek ona former visit there. I have also observed the occurrence 
of Limnophysa adeling in large numbers in a spot in San Lorenzo 
Creek at Haywards, one year only, not finding a single one before 
‘Orsince. 
Next to the great interior valleys the little county of San Fran- 
cisco shows a larger list of aquatic species than any coast county 
_ South of it, or any yet known in the Sierra Nevada. 
__ 1. Limnosphysa palustris Zzzn., and varieties proxima Zea, nut- 
taliana Lea, rowelli Zryon. 
2. Limnophysa gabbi 7ryon and var. adelince 7; ryon. 
3. Limnophysa humilis Say. 
4. Limnophysa obrussa Say. 
(5. Physa diaphana Zryon. 
6, Physa virginea Gould. 
7- Physa gabbi 77yon and var. dorbignyana Lea. 
8. Planorbis tumens Carpenter (occidentalis 7, G. C). 
9. Planorbis ( Helisoma) ammon Gould (dwarfed). 
10, Planorbis ( Gyraulus) vermicularis Gould. 
11, Planorbis (Menetus) opercularis Gould. — 
m 
ty 
ne 
Ancylus fragilis Tryon. (Gundlachia?) 
