THE NAUTILUS. 9 
By the perplexing variability of some members of this group, it is 
too unsafe to establish new species upon a few specimens coming 
from a single locality. 
The headquarters of these smallest Bivalves, and so probably of 
Spherium, are the region of our great lakes, which, in fact, seems to 
be the richest on the globe. And here, too, a serious difficulty is 
added to the one already lying in the embarassing richness of forms 
itself. The deep water mussels are decidedly different from the 
shallow water and shore forms, reduced in size, and less character- 
istic in shape, striation, color, hinge formation, ete., hence the double 
difficulty in ascertaining their true relations with the shallow water, 
river, pond and shore forms on the one hand, and among themselves 
on the other. Such is the teaching of the materials brought up so 
far from some deeper places of the lakes, mainly by the efforts of 
the Michigan Fish Commission, as I understand, upon the encourage- 
ment of Mr. Bryant Walker. There also is a field for successful 
work; the use of the dredge. | 
Another point may as well be mentioned here. It isan open ques- 
tion how far Cycladide are able to exist in brackish water, of rivers 
and creeks emptying into the sea, and in salt marshes. Conchologists 
having chances to collect in such places are invited to pay the matter 
their attention. The researches may be extended to other fresh 
water mollusks at the same time. 
A few hints must be added for those collecting and sending 
Pisidia (and Spheria). 1. Not even the smallest specimens should 
be overlooked, as some forms are very minute, and the young of all 
are of interest and value. 2. It is not only annoying, but really 
perplexing and deceptive, to examine lots where a part of the spec- 
imens had been picked out previously. Thus the larger, mature 
and characteristic examples of one or several species may be want- 
ing, while the younger and poorer are represented in the remnants. 
Whole suites only can afford a true conception of a species, variety 
or local form. Mixed lots, however, are the most desirable for 
examination, separated only for considerable differences in size of 
the specimens. 
Several conchologists lately have sent living Pisidia, which arrived 
alive and could be kept alive for some time, observed and examined 
for the soft parts. I would solicit the sending of more such. They 
should be packed up with damp moss, or other similar material, in 
receptacles admitting air, not in tightly corked vials. 
