190 NOTES ON SOME FRESH. WATER SHELLS. 



having as much surface as the foregoing clam, I have specimens weighing 

 almost three pounds, while the other hardly ever weighs more than one. 

 This shell is the commonest mussel of the west, and occurs wherever it can 

 get a foothold. In seme mussel-beds, the individuals are numbered by the 

 thousand. This clam may be easily recognized by its rough shell and its 

 weight. 



But the western shells are not all large. The Unio perplexa is indeed 

 smaller than most of our own shells. The peculiar lobe on this shell is pres- 

 ent only in the female, the male lacking it altogether. This shell rarely 

 occurs larger than this. 



This ruggad shell with the rectangular outline is called the Quadrula 

 cylindrica. When not worn, the shell is very handsome, being maiked with 

 dark green triangles like a tent olive. The animal within this shell is yel- 

 lowish, with an orange foot and black mantle. When living, this shell stands 

 high out of the mud, or lies horizontal upon it. 



One shell interesting, not for its color or size, but for its numerous va- 

 riations, is the Alasmodon rugosa. It occurs throughout the west, and also 

 in the Hudson River.' In some rivers it is large and heavy, as in the Spcon 

 River, and in others small and thin as in the Clinch River. In some rivers 

 it is black, and in others greenish. Sometimes it has stripes, and sometimes 

 none, but it may always be recognized by the undulations near its siphon 

 end. The meat is orange. 



The Alasmodon truncata also occurs in the west. It has a very thin 

 shell, and a peculiar truncated shape. The meat is orange. 



One mussel from Georgia has three or four spines projecting outward 

 from its valves. It is rare and local. 



There is another group of mussels called the Anodons, which have thin 

 shells, and are more adapted for living in ponds and quiet waters than in 

 braving the swift rivers. This shell, the Anodon suborbiculata, is one of them. 



We New Englanders can scarcely realize in what numbers clams can 

 occur in favorable localities. In some western rivers there are beds of acres 

 in extent, numbering thousands of individuals. Wherever there is a foothold 

 strong enough to admit of the shells resisting the high tides, there is a clam. 

 They generally seem to prefer rather shallow Avater. Sometimes, indeed, they 

 occur in water so shallow that when a low tide comes, they are all killed. 

 A friend of mine told me of a river, the banks of which were lined for ten 

 miles with clams killed in this way. They were so thick one could walk 

 the whole ten miles without stepping off a shell. 



The only value of clams is in the pearls they sometimes contain, and 

 in their ability to be converted into buttons. The pearl fishery is a great 

 industry on some western rivers, and many valuable pearls are taken out 

 every year. 



