482 Annals of the Carnegie Museum. 



or strong canvas, twill, or jean. The "Holland dredge" {cf. Memoirs 

 Carnegie Museum, Vol. IV, p. 281) modified, with a small wheel on 

 each side of the frame, will prove very serviceable. 



A good deal of dredging has been done in European lakes, and many 

 deep-water species, or forms, especially of Pisidium, have been 

 brought up in this way. It is time that we explore our lakes, especially 

 the Great Lakes. To judge from what has been secured by some 

 dredging in Lake Michigan good results may be expected. Some 

 deep water mollusks have also been taken from the stomachs of white- 

 fish, and it seems worth while to follow that trail. 



From dead leaves, moss, etc., specimens may be picked out, or a 

 portion of such material may be taken along; or better still, if water 

 is near, carried to it and its contents washed out. Such material may 

 also be dried and then its contents secured by sifting. 



On gravelly bottoms of rivers and creeks, where the net cannot be 

 directly used, there are other methods of procedure. Where there 

 is a strong current in shallow water, as on bars and riffles, a hole a 

 foot or two deep may be dug out; above it some furrows converging 

 and leading into it are made. Then the gravel upstream over a 

 wide stretch should be well stirred and the current will carry the 

 smaller and lighter particles down. From the hole the material thus 

 gathered is then taken out with the net and washed. If there is any- 

 body to help, the net can be held in the lower furrow to take up what the 

 current carries along. In this way large numbers of specimens not 

 otherwise obtainable can be secured, often representing rare species, 

 e. g., Pisidium cruciatum (2 mm. long), also various small gastropods 

 and very young Naiades. By the way, the same method may be 

 used for collecting certain Crustacea, insects, etc. 



When the water in rivers is quite low, there may be isolated pools 

 and waterholes along the shore where mollusks are aggregated in 

 great numbers, principally snails. There they sometimes can be 

 gathered by the quart. Not only a good supply of the larger forms 

 should be taken along, but the net should be used to secure the smaller 

 and minuter specimens. 



Seasons. 



Collecting may be done at any time of the year, even in mid-winter, 

 and good things have even been secured with the net through holes 

 cut in the ice. For obvious reasons, most may be accomplished in 



