FRESH-WATER MUSSEIvS AND MUSSElv INDUSTRIES. 35 



NONCOMMERCIAIv SPECIES. 



We have completed the list of mussels of some economic value, numbering about 

 41 in all. There are approximately 533 species of the Unionidae in North America 

 (Simpson). Therefore, though granting a few omissions in the present list for species 

 from localities little studied, it is discovered that the great majority of the American 

 species are not of economic use. It is desirable to mention only a few of those forms 

 which are most abundant and most familiar to shellers, or of particular interest for 

 other reasons. Most of the noncommercial species are not numerous, and some are 

 quite rare and restricted in distribution. Even in the economic investigations of 

 fresh-water mussels it is necessary to devote some attention to the useless forms, because 

 the study of such mussels often throws significant light upon the propagation, habits, 

 and other relations of the economic forms. 



The floaters, Anodonta grandis (Say) (PI. XXIV) and other species, and the slop- 

 bucket, Anodonta corpulenta (Cooper), are familiar shells of the slack waters along river 

 shores or in sloughs. The shell is very thin and brittle and entirely useless. In one of 

 the overflow lakes near Fairport there are found numbers of the very large and com- 

 pressed Anodonta suhorhiculata (Say) (PI. XXVI). The most interesting species of 

 Anodonta is the small, elongate, and paper-shelled Anodonta imbecillis (Say) (PI. 

 XXV), which has been found to develop without parasitism. 



Another species which has been observed to develop without parasitism, but which 

 has also been found to develop with a stage of parasitism on fish, is the squaw-foot, 

 Strophitus edentulus (Say) (PI. XXV), which is widely distributed in the Mississippi and 

 Atlantic drainages. The Anodontas are not only thin-shelled but also are marked by the 

 entire absence of hinge teeth ; Strophitus has no teeth but a thickened hinge line. The 

 shell is thicker than that of Anodontas but is too thin for commercial use; the nacre is 

 generally of a dirty-yellowish color. 



The spectacle-case is a thin-shelled mussel of the elongated form suggested by its 

 name. The species is Margaritana monodonta (Say) (PI. XXVI), of the Ohio, Cum- 

 berland, and Tennessee systems, but rare in the Illinois River. Its interest consists 

 in the fact that it is the nearest relative of the river pearl mussel, Margaritana margar- 

 itifera (Linnaeus) (PI. XXIV), the principal pearl-bearing mussel of Europe and New 

 England. 



The paper-shells, as the name indicates, are too thin for utility, although of attrac- 

 tive appearance. They are very common and of wide distribution through the Missis- 

 sippi Basin and elsewhere. The principal species are Lampsilis gracilis (Barnes) and 

 Lampsilis {Propter a) Icevissima (Lea). 



Just as there are minnows among the fishes which are very small, even when adults, 

 so there are small forms of mussels; an instance is afforded by the rainbow-shell, men- 

 tioned on an earlier page. One of' the smallest of all true fresh-water mussels is 

 Lampsilis parva (Barnes) , which grows abundantly in the ponds at the Fairport station. 

 It is narrow in form and never attains a length much exceeding i inch. Much of the 

 skepticism of practical men regarding the results of investigations of the life history of 

 mussels has been due to a lack of acquaintance with the small species. Time and 

 again shellers or others have found reason to believe that mussels bring forth their 

 young in an advanced stage of development, because they have found supposedly 

 young niggerheads attached to, or inclosed within the dead shells of old niggerheads. 



