T02 Ci)icinnati Society of Natural History. 



52. Unio retusa, Lam. 



L. \ x / 2 , H. \y^. Nacre white on margin but dark purple 

 within. 



53. Unio ridibunda, Say. 



L. i}(,H. j}£. Male of No. 60. Has a double row of teeth 

 projecting from lower posterior margin. 



54. Unio rubiginosa, Lea. 



L. 2^, H. 2. Like No. 63 but more compressed. Nacre 

 generally a light salmon color. 



55. Unio sayii, Tappan. 



L. i> l /2, H. 1^. Dirty straw color. 

 56 Unio securis, Lea. 



Compressed, yellowish green, peculiarly rayed with interrupted 

 light and dark spots. Female thicker. 



57. Unio solida, Lea. 



Heavy var. of No. 37. 



58. Unio sub-ovata, Lea. 



L. 4^, H. Ventricose rayed with green on poste- 



rior. 



59. Unio sub-rotunda, Lea. 



L. i%, H. ij4- Interrupted dark rays near beaks disappear- 

 ing in old specimens. Male more elliptical. 



60. Unio sulcata, Lea. 



Female of No. 53. Resembles female of No. 50 but the shell 

 is thicker and more globose. 



61. Unio tenuissima, Lea. 



L. 3*^, H. \Y%. Compressed, thin, green, rayed with darker 

 green stripes. 



62. Uhio triangularis, Barn. 



L. 1^, H. 1. Very triangular, ventricose beautifully rayed 

 with interrupted green stripes. 



63. Unio trigona, Lea. 



Sometimes like No. 37, but has no rays and very slight sulcus. 



64. Unio tuberculata, Barn. 



L. 2^, H. 1^. Entire surface covered with tubercles. 



65. Unio undulata, Barn. 



Variety of No. 46, but has more ridges or plications. 



