250 THE AMERICAN MIDLAND NATURALIST 
any of the Anodontinae on account of its sculpturing on the pos- 
terior dorsal ridge, the costae there being somewhat similar to 
those on the shell of some Amblemae or Quadrulae. Simpson 
treated this genus under three sub-genera and while the shell 
characters may greatly differ, yet, the animal characters are so 
constant and the known species are so few to retain this subgeneric 
treatment. ‘The type, S. compressa (Lea), is not found in this 
state—not even in the Mississippi River. Only two species of 
this genus, S. complanata (Barnes) and cosiata (Rafinesque), are 
found in Missouri and they are not widely distributed, the former 
being confined mostly to the north and the latter to the south 
part of the state. 
Symphynota complanata (Barnes). 
(‘‘Heel Spitter,’’ ‘‘Hackle Back,’ ‘‘ Hatchet Back,’ “‘ Pan-cake.’’) 
| Pl. XXII, Figs. 70 A and B. 
1823—Alasmodonta complanata Barnes, Amer. Jour. Sci. and Arts, 
D2 710) (pls SU hipeyon. 
1900b—Symphynota complanata (Barnes) Simpson, Proc. U. S. Nat. 
Mus., XXII, pp. 665-666. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Branchial opening thickly set 
with short papillae; anal finely dentate; anus of intestine fringed 
with three or four papillae; supra-anal large, mantle connection 
widely separating it from anal; inner gills, wider than outer, 
inner laminae free except briefly, anteriorly; marsupia occupy 
entire outer gills, truncated along ventral margin when charged, 
ovisacs not divided; glochidium very large, spined, hinge line 
undulate measures 0.310 x 0.320mm; most of soft parts yellowish, 
gills rusty color when gravid. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Usually rhomboidal, compressed; 
alae high, marked with a few upcurved costae; disk smooth; 
beaks low, sculptured with coarse double-looped ridges; epidermis 
of young shell reddish with brown rays; of old specimens, brown 
to black. 
INTERNAL STRUCTURES:—Cardinals single in right, double in 
left valve; laterals faintly double in both valves; umbonal cavity 
shallow; nacre bluish to satiny white with marginal ribbon of 
