.X 



36 NAIADES OF MISSOURI 



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 raripliplicaia from the 

 synonomy of Simpson's Ouadrula 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. 



184 1 — Unio perplicatiis Conrad, Pr. Ac. N. Sci. Phila., I, p. 19. 



1900 — Quadrida perplicata Simpson, Proc. U. S. Nat. Mus., XXII, 



p. 767. 

 1912b — Credononta perplicata Ortmann, An. Car. Mus,. VIII, p. 247-248. 



SHELL CHARACTERS. 



External Structures: — vShell 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 



d^ 115 X 80 X 48mm (Osage R., Osceola, Mo.,) 



9 90 , X 66 X 46 " (,St. Francis R., Greenville, Mo.,) 



9 83 X 67 X 48 " (Osage R., Linn Creek, Mo.,) 



cf 16 X 14 X 10" ( " " Warsaw, Mo.) 



Many juveniles taken in the Osage average as the above 



