Che Conchologsts Exchange. 
COPYRIGHT SECURED 
Wot. sD: 
CHESTNUT HILL, PHILA., PA.. MARCH AND APRIL, 1887. Nos. 9 & 10 
Redd Afpn -30/6% 
A Publication Designed for Conchologists and 
Scientists generally. 
ISSUED MONTHLY 
BY 
We AY EIREL TL, 
Eovitor AND PuBLisHER. 
Jia> Correspondence upon Conchology, as well as 
reliable items of interest concerning the Mollusca, their 
habits, localities, etc., kindly solicited from all. 
Matters for publication must be received by the 
fifth of each month. 
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Address all correspondence to 
WM. D. AVERELL, 
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Chestnut Hill. 
Philadelphia, Pa., U.S. A. 
REDUCTION IN ADVERTISING RATES. 
One inch, displayed, 1 month ........-.... =$) 50 
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HE liberal inducements placed before 
you in the handsome PREMIUM 
LIST, found in another column, should 
enliven your interest in “The Conchologists’ 
Exchange” and make it what we propose 
it shall be at all hazards—the most successful 
paper of its kind in the country. 
E present our readers with a double 
number this time; those for March 
and April being combined in order 
to more comfortably provide for futurg issues. 
It is proposed to make the number for May 
twelve pages in size, instead of eight as here- 
tofore, and to have it well on its way to our 
readers by the 15th of the month. 
EROSION OF FRESH-WATER 
SHELLS. 
BY REV. WM. M. BEAUCHAMP. 
(No. II.) 
T may prove a mistake to suppose that the 
erosion of shells is caused by the presence 
of lime in the water, and I judge itis often- 
er due to the emission of carbonic acid gas from 
plants acting upon the lime of the shell. Se- 
neca River in New York, flows fora long dis- 
| tance through gypseous shales (sulphate of 
lime), and its shells are but moderately eroded, 
though affected by vegetable coating. In Onon- 
daga and Cross Lakes, in the same formation, 
living shells are rarely eroded, while dead 
| shells soon become rotten in the abundant marl. 
| On the other hand Beaver Lake, a shallow pond 
amile from and above the level of Seneca 
River, produces Unio complanatus, small and 
| much eroded, and the large Anodonta fragilis 
_ is often worn entirely through the beaks. The 
pond has mucky shores and is filled with water 
weeds. Oneida Lake, 22 miles long, shallow, 
andina level country, is another case in point. 
It is difficult to find a fair specimen of Unioni- 
de there, and at its outlet the little Uz70 Mowr- 
Eboraci is very Wadly eroded. Still further 
north and ina sandy region, Salmon Creek fur- 
nishes A/edantho decisus with the apex squarely 
cut off, a rare thing in this part of the country. 
