6 NAIADES OF MISSOURI 



physiographic provinces because of their different ecological 

 conditions, namely, the muddy, sluggish streams of the north, 

 swift, clear-water streams in the south and the mediocre streams 

 of the Central portion: — 



a = Prairies; h = Mo. and Miss. R's (Proper); c = Ozark Uplift. 

 I.— NORTH MISSOURI = Primitive Mussel Fauna. 



I. a — New Prairies, or Glacial Plains. (N. and N.W.Mo.) 

 i.b — Missouri-Mississippi Flood-plains = Mo. Lakes and Miss R. 

 (Proper) to mouth of Mo. R. (N. E. Mo.). 

 Mo. R. (Proper) = Depauperated Mussel Fauna. 

 II.— CENTRAL MISSOURI = Intergraded Mussel Fauna. 

 2. a — Old Prairies of W. Central Mo. 

 i.c — Ozark Border, or North Slope. 

 III.— SOUTH MISSOURI = Modern Mussel Fauna. 

 2.C — Ozark Plateau. 

 3.C — Ozark Center, or South Slope. 

 2.b — Miss. R. (Proper) below mouth of Mo. R. and Miss. 



Lowlands of S. E. Mo. = Depauperated Mussel Fauna. 



The vSpccies and Sub-Species, Hsted under the following 

 general Key to the Missouri Naiades, arc assigned to the different 

 sub-physiographic provinces where they predominate by employ- 

 ing to the extreme right after their names the lettered numbers of the 

 above Classified Account: e. g., Amblema rariplicata (Deshayes) — 

 l.a., — thus indicating the New Prairies Fauna where mostlv 

 found. 



General Key for Identification of the Missouri Naiades. 



This key is for very general use, being based upon the essential 

 reproductive and nutritive characters of the animal parts for 

 the Families, vSub-I'amilics and Generic Groups. These characters 

 arc indicated under the lettering in the Scheme below and the 

 enumeration of all Naiades for Missouri is denoted both by the 

 Roman and Arabic numerals. The geographic distribution of the 

 Species and Sub-Species is indicated by the lettered numbers. 

 The following Scheme of progressive classification is employed: — 



A.— FAMILY I. 



(A).— Sub-Family (I). 

 a. — Genus I. • 



(a.) — Generic Group and Sub-Genus (I). 

 I. — Species. 



(i). — Sub-Species. 

 A. — Gills with no water-tubes, septa incomplete, obliquely arranged; gill- 



