THE AMERICAN MIDLAND NATURALIST 



SUMMARIZED DISTRIBUTION OF MISSOURI MUSSELS. 



In comparing with other lists of Naiades, mostly secured by 

 the writer in correspondence with students for the surrounding 

 States, it is found that North Missouri is mostly that of the Mussel 

 fauna of Illinois and Iowa; that South Missouri belongs to the 

 great South-West, i.e., Arkansas, Oklahoma, Louisiana and Texas 

 and that ( 'eniral Missouri is really a combined or transitional zone 

 for these two sections of the Mississippi Valley. The Numbers 

 in the second column of the following comparative lists represent 

 those Species of the writer's list for Missouri that are identical with 

 those of the lists most representative of the Upper Mississippi 

 and the South- West: — 



/ ' pper Mississippi 



No. Species in Illinois (W. S. Strode's List) 1 29 



No. Species in Iowa (T. Surber's List) 42 



South- West 



No. .Species in Ark. (H. E. Wheeler's List) 50 



No. Species in Miss. & Tex. (L. Frierson's List) 2 .. ..25 



No. Species in Okla. (B. F. Isely's List) 3 29 



No. Species in La. (Vaughan & Frierson's List) 43 



North Missouri 

 No. in common.. ..29 

 No. in common. ...40 



South Missouri 

 No. in common. ...26 

 No. in common... 1 5 

 No. in common. ...29 

 No. in common.... 21 



Many peculiarities are noted in the Naiadgeography oj Missouri. 

 It is surely a geologic paradox to note a predominance cf primitive 

 species oj Xaiades, in the New Prairies, or Glacial Plains. Another 

 problem to be worked out is that of the reason for the limitation 

 of the distribution of Elliptio dilatata, Nephronaias ligament ina 

 and Strophitus edentulus, — Species of the widest and most general 

 distribution in other States. While 5. edentulus is one of the com- 

 monest of shells for Central and South Missouri, yet its occurrence 

 is very doubtful for North Missouri, as the author, in his more 

 thorough investigation of this more accessible part of the State, 



l W. S. Strode, Nautilus, V., p. 61 , Oct, 1891; IX, pp. 115-116, Feb. 1896. 

 2 L. S. Frierson, Nautilus, XXIV, p. 134, Apr. 191 1. 



3 F. B. Isely, U. S. Bureau Fis. Doc. No. 792, pp. 1-24, 1014; U. S. 

 Bu. Fish. Econ. Cir. No. 9, Feb. 17, 1914. 



