52 MUSSELS OF CUMBEELAND EIVER AND TEIBUTAEIES. 



31. Obovaria retusa (Lamarck). Golf-stick. 



Although we obtained only a few specimens of this species, scattered valves were 

 frequently found alor.g shore, and there is reason to believe that it is considerably 

 more common than our small collection would indicate, although by no means 

 abundant anywhere. In the Cumberland it attains a rather large size, our largest 

 shell measuring 68.5 mm. long, 74.5 mm. high, and 46.9 mm. in diameter. It is a 

 heavy and solid shell, but the deep purple of that portion of the nacre within the 

 pallial line makes it valueless for buttons. All our shells are somewhat eroded at 

 the umbones. Two of them are considerably less retuse than the others, somewhat 

 approaching 0. circulus in this respect. All have the epidermis somewhat paler 

 posteriorly, but not so markedly so as is usually the case with 0. circulus. 



32. Obovaria circulus (Lea). 



Rather common in the main river from Bumside to Half Pone Bar. This species 

 produces too small a shell to be of much importance to the button trade. The larger 

 shells would funiish two or four blanks apiece, and are excellent both as to material 

 ar,d thickness. The nacre seems to be unusually durable and retains its firmness and 

 luster long after others have become chalky. 



33. Obovaria ellipsis (Lea). Missouri niggerhead. 



This species is chiefly northern in its distribution and does not attain large size in 

 the Cumberland. Although in its shell characters it bears considerable resemblance 

 to some of the Quadrulas, especially the niggerhead, Q. ebena, it is really more closely 

 related to the sand-shells. Where it attains large size it is an excellent button shell 

 and would be a fine species to propagate, but the reduced size of the shell in the 

 Cumberland indicates that the conditions there are not favorable. We found gravid 

 examples above Clarksville early in June. 



34. Plagiola securis (Lea). Butterfly. 



This species is fairly common throughout the entire length of the river below the 

 falls, and, while not abundant enough to make a large percentage of the shells taken for 

 commercial purposes, it makes a fair sprinkling in most of the clammers' piles. It 

 seems to thrive exceptionally well in the Cumberland and is more common here than 

 in most rivers. The shell, especially of young to medium-sized, well preserved males, 

 is one of the most attractive among the Unionidse. In the Cumberland there is a 

 marked difference between the shells of tlie males and females, that of the former being 

 flat and compressed and of rather vmiform thickness, while those of the females are 

 much more tumid and swollen. The measurements of a fairly typical male (F5086) 

 of medium size are 54 mm. long, 44 mm. high, and 21.1 mm. in diameter, while those 

 of a tumid female of about the same length (F2660) are 55.3 mm. long, 45 mm. high, 

 and 33.7 mm. in diameter. In the lower part of the river the nacre is somewhat 

 spotted, but upstream the shells are free from stain. On account of its excellent 

 luster, flatness, and uniform thickness, this is an excellent button shell, the males 

 being much superior to the females. 



Females were found gravid May 29, and were in the height of the breeding season 

 from about June 3 to 16. This would be a very valuable species with which to stock 

 the river. 



35. Plagiola elegans (Lea). Deer-toe. 



This species is not as common nor as widely distributed as the preceding. Large 

 shells can be used in the manufacture of buttons, but the great majority are too small. 

 The largest example found was a single valve 59 mm. long, picked up at the foot of 

 Gowers Island. The beautifully tesselated green markings on the epidermis make 

 it an attractive shell when perfect. 



