118 THE AMERICAN MIDLAND NATURALIST 
no tendency toward posterior biangulation. Perplicata, being 
more of a southern form, is not found in this state north of the 
Missouri, while rariplicata, a more northern shell, is mostly con- 
fined to North Mo., where it is the predominant species of the 
Amblemae, yet it is found occasionally in Central Missouri. 
Mr. Bryant Walker, who has rescued raripliplicata from the 
synonomy of Simpson’s Quadrula plicata, has recognized the 
North Missouri “‘ plicata’’ as Deshayes’ shell. The habitat of this 
species is that of muddy bottom with a substratum of limestone, 
of deep and quiet water and prefers muddy rivers to that of clear 
creeks. It is found in the Mo. Platte, Grand R., Big Tarkio and 
occasionally in their larger tributaries. It has never been found 
in any of the lakes. Its breeding season is very short, having 
been found gravid only in June. 
Amblema perplicata (Conrad) 
(“Blue-Point,”’ “’Three-Ridge,’’ ‘‘ Round-Lake.’’) 
Pl. XVI. Figs. 37 A and B. . 
1841— Unio perplicatus Conrad, Pr. Ac. N. Sci., Phila., I, p. 19. 
1900—Quadrula perplicata Simpson, Proc. U. S. Nat. Mus., XXII, 
Re ee perplicata Ortmann, An. Car. Mus,. VIII, p. 247-248. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES :—Shell ovate, or obliquely, quadrate, 
medium in size, moderately inflated, greatest inflation at center 
of disk; beaks low concentrically sculptured with two or three 
loops at foot of post-umbonal ridge; posterior end of shell biangu- 
lated, 5-6 coarse plications across post-half of shell parallel to 
antero-postero axis; costae on rounded, post-dorsal ridge few, 
broad; epidermis black. 
INTERNAL STRUCTURES:—Cardinals double in both valves; 
interdentum long and broad; laterals single in right, double in 
left; muscle scars deeply impressed; nacre white with posterior 
surface bluish to lavender, irridescent. 
Sex Length Height Diameter Locality 
O Wis, x sOeuxke Asmm (Osage R., Osceola, Mo.,) 
O90" xX 60> x AG) (St. Francis R., Greenville, Mo.,) 
O.-837" X67" x) TAB ee (Osage R., Linn Creek, Mo.,) 
OW 6 tx “raed | roy 2? Cea ” Warsaw, Mo.) 
Many juveniles taken in the Osage average as the above 
