62 MUSSELS OF CUMBERLAND RIVER AND TRIBUTARIES. 



75. Quadrula ■pyramidaia (Lea). 



Rare; we obtained a few examples in the vicinity of Mill Springs Bar. Our speci- 

 mens have a broad furrow on the posterior half of the shell and differ from Q. obliqua, 

 which they otherwise much resemble, by the umbones projecting far forward. They 

 agree quite closely with Conrad's figure and description ° of Unio mytiloides which 

 Simpson regards as a synonym, except that the epidermis of our shells is black rather 

 than brown and umbones are badly eroded. 



This is a ver>^ perplexing species. The extreme form, which, if it were only con- 

 etant, would represent a very well marked and easily recognizable species, resembles 

 an immensely overgrown Pleurobema clava in general appearance. Such specimens 

 are rare; we have a few in the Washington collection. Our shells represent a sort 

 of intermediate form between that and Quadrula ohliqua. 



Mr. Boepple obtained examples from several stations in the upper river, to which 

 portion it is apparently pretty well confined. 



7G. Quadrula subrotunda (Lea). 



The young of this species have a general resemblance to Quadrula ebena, the 

 niggerhead, but can be distinguished by their polished epidermis and broken rays 

 near the umbones. We obtained only a few examples of these easily recognized 

 shells. 



What is probably the adult of this species is occasional through the length of the 

 river. We have not been able satisfactorily to connect the small shells with the large 

 ones through a perfectly imbroken series, but up to the present can think of no better 

 disposition to make of them. They have a black epidermis, with the umbones 

 generally more or less eroded, and very much resemble an elongated ebena. These 

 large shells are fairly common in the upper stretches of the river. A peculiarity of the 

 old mussel is the rich orange color of the soft parts. At the blank factory at Clarksville 

 they are known as the "long solid" and are regarded as one of the best button species 

 of the river. None were found gravid. If they were to prove amenable to propa- 

 gation, they might be profitable to plant in the upper part of the river and in similar 

 situations where ebena would not thrive. 



77. Quadrula ebena (Lea). Niggerhead. 



This important commercial species, which is generally regarded as the producer 

 of the most valuable shell for the manufacture of buttons, is absent in the upper Cum- 

 berland, and is abundant enough to be of considerable commercial importance only in 

 the lower stretches of the river. 



The niggerhead is a deep-water shell and is rarely found in small rivers, or in such 

 mussel beds as are found in shallow water. It seems in general to prefer mud to sand 

 and gravel, and the percentage collected depends much upon the methods of collect- 

 ing. Work in deep water will bring to light a larger percentage than wading or gath- 

 ering by hand or a rake. 



The breeding season in the Cumberland begms in May and extends through the 

 greater part of June, perhaps longer. In this species the condition of the development 

 of the young can be roughly estimated by the appearance of the gill. When tlie ova 

 pass down into the gill they are at first red, or carmine, probably because of an abund- 

 ance of food material; as the glochidia develop they gradually fade out until the gills 

 of a fully ripe niggerhead are of a dirty white color. 



There is not much variation in shape among the shells, some being elongate and 

 others more rounded than the average. The shells show very little erosion, and the 

 young exhibit the peculiar white patch near the umbone, as has been fully described 

 by Lea. Tlie nacre is rather frequently stained bro^vn, and nearly all lack uniformity 

 in thickness, the shell thinning out somewhat abruptly a little behind the middle of 



o Conrad, Monograph, p. 41, pi. XX, 



