THE NAUTILUS. 



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 

 Sphcerium, 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, etc., 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 a* well be mentioned here. It is an open ques- 

 tion how far Cycladidce 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 

 Pisiilia (and Sphceria). 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. 



