68 MUSSELS OF CUMBEKLAISTD RIVEE AND TRIBUTAEIES. 



Where it attains its best development, the buckhom is an excellent button shell, 

 indeed one of the best. It does not find the most favorable conditions for growth and 

 development in the Cumberland, however. It is not as yet amenable to propaga- 

 tion on a large scale, as it is but rarely that one finds gravid examples. 



60. Quadrula perplicata (Conrad). 



The plicate Quadrulas of the Cumberland, especially the middle portion of the 

 river, are rather peculiar shells, lying somewhere between typical plicata and undu- 

 lata. The beaks are too low and flattened for plicata and the shells are too heavy 

 and a trifle too inflated for undulata. A marked feature about them, in addition to 

 their general rotundity of outline, is the fact that they usually taper to a point posteri- 

 orly. The clammers call them the "round-lake," and say that in proper conditions 

 they are good pearl bearers. The folds are few and gently rounded. Mr. Bryant 

 Walker, who examined them, is of the opinion that they are perplicata. We obtained 

 some good specimens at Meeks Spring bar. Our largest measures 119 mm. long, 86 

 mm. high, and 56 mm. in diameter. At Half Pone bar a particularly interesting and 

 instructive lot of young shells were obtained. These are inflated and rotund, 

 approaching a spherical form with a greenish epidermis. Though quite small, they 

 are so worn at the umbones that they look like old shells and no beak sculpture is 

 shown. The smallest measures 17 mm. long, 15 mm, high, and 10 mm. in diameter. 

 Farther up the river, at Cloyds Landing, this shell approaches undulata, while in 

 Stones River, near Murfreesboro, the real undulata is found. 



The shells are thick, solid, and heavy, but the nacre is spotted and they form rather 

 poor button material. If they could be obtained free from spots, they would have a 

 good market value. 



61. Quadrula undulata (Barnes). Three-ridge or blue-point. 



Beautiful examples of this species are common in the West Fork of Stones River 

 near Murfreesboro, Tenn. It is also found in the East Fork near Walterhill. The 

 young examples are yellowish brown, well compressed, and entirely free from erosion, 

 so that the umbones show the sculpture very plainly. This consists of four or five 

 high, coarse ridges, the first-formed ones crescentic, the older ones gradually vanishing 

 backward until the last one is a short, low tubercle. The undulations are deep and 

 crossed by numerous small furrows. A noteworthy feature of these shells is the great 

 distance of the pallial line from the margin. The shells are somewhat spotted, but 

 the spots are small and they would yield a fair amount of good button material. 



62. Quadrula heros (Say) . Washboard. 



This is a species of large rivers. It is not found in the upper part of the Cumberland, 

 but is abundant in the lower river. The first we saw was at the Mill Springs bar. 



This species bears the largest and heaviest shell of the North American Unionidae. 

 It becomes rather large in the Cumberland, but not as immense as in the Wabash and 

 some parts of the upper Mississippi. Our largest shell measures 162.8 by 115 by 62.4 

 mm. Our collection exhibits little variation. From the unusually large number of 

 small examples seen it appears that the species is exceptionally prolific in the Cum- 

 berland, especially about Half Pone bar and Owl Hollow bar above Clarksville. 

 All our examples are somewhat eroded at the umbones, but only two or three badly. 

 The young examples are noteworthy for having the finely waved broken sculptures, 

 characteristic of the umbones of the older specimens, over the entire disk and the 

 plications rudimentary or only faintly developed, so that they do not closely resemble 

 the old. 



We found no gravid examples. They are indeed very rarely found, and nothing 

 is known at present about its spawning habits or as to what fish acts as host to the 

 embryos.a 



a Since the above was written investigators at the Biological Laboratory at Falrpqft tiave thrown 

 considerable light on the breeding habits, hosts, etc., of this species. 



