MUSSELS OF CENTRAL AND NORTHERN IV^NNESOTA. 13 



on each valve, at other times the whole interior of the shell is dis- 

 colored. The stain usually affects only the interior layer or coat of 

 nacre and when this is removed the rest of the shell is perfectly clean 

 and uninjured. Such spotting of the shell, of course, injures their 

 commercial value and reduces the material to the second or third 

 grade. In other respects the shells have a fine luster and good tex- 

 ture, and would make excellent button material. 



PEARLS. 



A few pearls and about the usual number of slugs were obtained 

 from the carload of shells sent from Fergus Falls. At Little Pine 

 Lake we also received reliable information that pearlers had worked 

 the Red River above Mud Lake two years before, and that they 

 obtained an abundance of mussels, with a fair amount of pearls. 

 Further than this there has been no search for them in the Red River. 

 If the discoloration noted above is due to some sort of parasite, it 

 would very likely affect the pearls and slugs as weU as the shells, 

 but no data could be obtained. There is no reason other than this 

 why the Red River should not be as prolific of pearls as the Mississippi. 



PROPAGATION. 



The conditions at Otter tail Lake are very favorable for the propa- 

 gation of certain species of mussels. The lake is 10 miles long by 4 

 miles wide, and is remarkably clean and free from weeds. It is sur- 

 rounded also with fine sand and gravel beaches and contains many 

 large sand bars. The Red River enters at the northeastern corner 

 and flows the entire length of the lake. Similar conditions exist at 

 Lost, West Lost, Pine, and Little Pine Lakes, but the lakes them- 

 selves are much smaller. At little Pine Lake the bottom was nearly 

 covered with CJiara and algae, but wherever there was a bare spot 

 the mussels were present in large numbers. As these lakes are 

 full of just the kind of fish to serve as hosts the conditions are ideal 

 for mussel propagation. On the river itself the conditions are less 

 favorable. There are several dams in Fergus Falls, and a large 

 power dam, 36 feet in height, 4 miles below the city. None of these 

 dams are provided with suitable fishways, so that they form an 

 effective barrier to the ascent of all fish. 



RECOMMENDATIONS. 



1. Evidently the first thing to be done is to determine the cause 

 of the stains which are so abundant. A satisfactory solution of this 

 question would be of immense practical value, not merely here in the 

 Red River drainage but wherever mussels are found. Different 



