MUSSELS OF CUMBERLAND RIVER AND TRIBUTARIES. 



61 



Where the pigtoe is found in abundance, as in some parts of the upper Mississippi, 

 it is used quite extensively in the manufacture of buttons. It yields only a few 

 blanks per shell, however, and would not be a desirable species to propagate. 



71. Quadrula obliqua (Lemarck). Ohio River pigtoe. 



This is the most abundant, and, on this account, the most important, commercial 

 species in the river, especially in the central portion, where it greatly exceeds any 

 other species in number. 



The Ohio River pigtoe is a very good button shell. It is inferior to the niggerhead, 

 both in luster and form, the sulcus on the side and the thinning out at the tip making 

 it of unequal thickness; but, with the exception of the niggerhead, it is one of the 

 best species. 



It is a rather prolific breeder. We found more gravid specimens of this than of 

 any other species. The height of the spawning season is during the latter half of 

 May and the earlier half of June. Occasional examples, however, may be found 

 during the entire summer. Of five examined at Beasleys Shoals August 9, four 

 were gravid. The portion of the gills used as marsupia varies greatly in different 

 examples; it may depend upon the amount of ova fertilized and upon the age of 

 the mussel. In some of the mussels the lower half of the outer gills are filled; in 

 other cases the entire outer gills and quite frequently all four gills. Occasionally 

 three gills, the two outer and one of the inner, contain eggs or young. There are 

 no well-marked sulci between the conglutinates, which are rather thin and flat, 

 resembling the seed of the green cucumber in general appearance. They are peculiar 

 in that, when viewed from the side, they present a wavy appearance. This, so far 

 as we know, is found only in the present species and enables one to distinguish the 

 conglutinates even when found free from the animal. The wavy appearance is due 

 to little pits in the anterior and posterior faces. A conglutinate of this species was 

 found lying on the gravel bar in shallow water at Half Pone Bar June 16; the species 

 was therefore spawning at that date. 



Dr. Ortmann has removed this species from the genus Quadrula and placed it in 

 Pleurohema. All the examples he had examined up to that time had glochidia in 

 the outer gills only. According to the data given above, its transfer to Pleurohema 

 seems hardly advisable until the whole group is more thoroughly revised. 



72. Quadrula coccinea (Conrad). 



What appears to be an oblique form of Quadrula coccinea occurs rather frequently 

 in the Big South Fork opposite Parkers Lake Station. Similar forms occur in the 

 upper Cumberland down as far as Tear-coat Bar. In the main river these forms 

 run into others in inextricable confusion, and nothing definite can be said about 

 this specie* from the material at hand. 



Dr. Ortmann is of the opinion that Quadrula coccinea is a variety of Q. obliqua. 

 In some of the northern rivers it seems to be a fairly constant and well-defined form. 



73. Quadrula solida (Lea). 



Only occasional. We obtained a few, principally at Indian Creek Bar. The 

 shells were not typical and differed considerably from those found in the upper Mis- 

 sissippi. The sulcus is very faint, and the nacre is not white but varies from pale 

 rosy to purplish red. 



74. Quadrula plena (Lea). 



This appears to be a rare species in the Cumberland, and we obtained only a few 

 scattered shells. They are all small and resemble very closely a much-shortened 

 Q. obliqua, the compressed posterior portion being very short and the height of the 

 shell being very great, considerably exceeding the length. The nacre is pale rosy. 



Mr. Boepple obtained this species in 1910 from Fords Island down to Martinsburg 

 in the upper part of the river. 



