46 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; }—Mo. and Miss. R’s (Proper); c=Ozark Uplift. 
I—NORTH MISSOURI= Primitive Mussel Fauna. 
; 1.a—New Prairies, or Glacial Plains. (N. and N.W.Mo.) 
1.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. 
1.c—Ozark Border, or North Slope. 
IIIl.—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. EK. Mo.—Depauperated Mussel Fauna. 
The Species and Sub-Species, listed under the following 
general Key to the Missouri Naiades, are 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 mostly 
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, Sub-Families and Generic Groups. ‘These characters 
are 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 classiflcation is employed :— 
A.—FAMILY I. 
(A).—SuB-FAMILY (I). 
a.—GENuws I. 
(a.)—GENERIC GROUP AND SuB-GENUsS (I). 
1.—SPECIES. 
(1).—SuB-SPECIES. 
A.—Gills with no water-tubes, septa incomplete, obliquely arranged; gill- 
