56 MUSSELS OF CUMBERLAND EIVER AND TEIBUTAEIES. 



52. Alasmidonta truncata B. H. Wright. Elk-toe. 



This is not a common mussel in the Cumberlaud and is, generally speaking, a spe- 

 cies of rather small streams and the upper courses of larger rivers. All the shells 

 fomid were dwarfed, very thin and eroded, and with the epidermis rather badly 

 stained . 



When well developed this is an attractive shell, but it is always too thin and fragile 

 to have any commercial value. 



According to Mr. Bryant Walker, there is no difference between this and A. margi- 

 nata Saj'^, and our thin dwarf specimens lend probability to this view. As we have 

 seen but few marginata we have no means of comparing them. As Simpson has sepa- 

 rated the two forms, howeA^er, and ours are within the geographic range of truncata, 

 we retain for the present Simpson's name. 



53. Margariiana mpnodonta (Say) . Spectacle case. 



Occasional from Snows Island, where we first encountered it, as far down as Dover 

 and perhaps beyond. The shells are fragile and break and crack easily, and disap- 

 pear soon after dying. The species has no commercial value. 



54. Unto gibbosus Barnes. Lady-finger; spike. 



Unlike Unio crassidens this species is not especially abundant in the Cumberland. 

 Though distributed throughout the entire length of the river, at many stations only 

 a half dozen specimens were found, and nowhere did it rise above 4 per cent of the 

 entire catch. In the Cumberland above the falls it is about the only species found. 

 In the Clear Fork at Jellico, Tenn., and Savoy, Ky., it was abundant, forming about 

 90 per cent or more of the entire mussel population, and numerous dead shells recently 

 killed by muskrats were found along shore and at the base of the water-willows. 



These Clear Fork examples were all small dwarf shells with a rather pale nacre. 

 They approach a well-marked form found in Green River, Ky., and other southern 

 streams. The Clear Fork flows through sandy and shaly country and the water may 

 be too deficient in lime to promote good shell growth. Immediately below the falls 

 we encountered the normal full-gi'own form which is the one of the main river. 



Gravid examples of this species were found during the entire summer. 



55. Unio crassidens Lamarck. Elephant-ear. 



Exceedingly abundant, especially in the upper part of the river. It is a species of 

 large streams, and we did not find it in any of the tributaries nor above the falls. In 

 the upper part of the river this shell is a decided nuisance, forming a large part of the 

 clammer's catch, taking much of his time and labor and yielding little in return. It 

 is generally known as the "pink," and clammers, on their prospecting cruises, note 

 down the percentage of "pinks" and "whites," from which to judge the value of a 

 bed. It is the great abundance of this species that makes the section of river from 

 Burnside to Celina unprofitable clamming, and the problem of making this stretch a 

 valuable clamming ground consists as much in the reduction of this species as in the 

 increase of valuable kinds. 



U. crassidens exhibits considerable modification as one ascends the Cumberland. 

 In the lower stretches of the river most of the shells are the rather elongate form, 

 which seems to be most common the country over. As one advances upstream these 

 elongate shells gradually give way to a short and chunky variety. 



The shells from Half Pone bar and a few from Mill Springs and Salt Lick bar show 

 rather well-marked rays; most of the others are rayless. 



Occasionally shells with the nacye very pale or almost white are found. These are 

 called "white-pinks" and are acceptable to the buyer. Even the more or less 

 markedly pink ones are beginning to be used, but there is little demand for them and 

 they always bring a rather low price. The shells work up exceptionally well, being 

 soft and free from grit. 



