EXPLANATION OF PLATE XVIII. 



Fig's 45 A and B. — Q. qitadntla (Raf.) 9, Lake Contrary, St. Joseph. 



Fig's 45 C and D. — Q. quadrula cf . Same locality as female. 



Fig's 45 E and F. — Q. quadrula d', Flat Cr., Sedalia. 



Vig's 4.6 A and B.-Q. quadrula 9, L. Contrary. — A common pathologic 

 shell found in the N. W. Mo. Lakes, 



Frig's 47 A and B. — Q. quadrula contraryensis Utterback 9 , L. Con 

 trary. — A new variety. 



Fig's 48 A and B. — Q. fragosa (Conrad) 9, Miss. R., Hannibal. 



Fig's 49 A and B. — Q. aspera (Lea) 9, Osage R., Warsaw. 



