EXPLANATION TO PLATE 54. 



TENNESSEE RIVER. 



Group 26 (in part). Ijot 15L Iliwassee Island, Tenn. This plate of shells is composed 

 solely of individuals from lot 151 and is not a sample of the gi'oiip as a whole. They show the 

 gi-eat degi-ee of spinosity developed in loudonensis. Natural size. 



170 



J'} 



