THE NAIADES OF MISSOURI 325 
only represented in this State by ellipsis and that in a limited 
distribution both in the geographical and individualistic sense. 
Obovaria (Pseudo6n) ellipsis (Lea). 
(‘Missouri Nigger-Head,’’ ‘‘Egg Shell,’ ‘Hickory Nut.’’) 
Pl. XXV, Figs. 84 A and B. 
1828— Unio ellipsis Lea, Tr. Am. Phil. Soc., III, p. 268, pl. IV, fig. 4. 
1900b—Obovaria ellipsis (lea) Simpson, Proc. U. S. Nat. Mus.; 1912b, 
Ortmann, Car. Mus., VIII, pp. 323-324. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Branchial opening small with 
two-ranked papillae; anal finely papillose; supra-anal crenulated 
(a rare character) not well connected to anal; mantle border 
just antero-ventrad to branchial opening with crowded papillae 
or crenulations extending one-third of the way towards center 
of ventral margin; gills very wide, both blunt and pointed poster- 
iorly, inner laminae of inner gills entirely connected to visceral 
mass; palpi rather small, connected about one-half of their length 
antero-dorsad; foot pinkish, mantle edge dark in region of siphonal 
openings, rest of soft parts dirty white. 
REPRODUCTIVE STRUCTURES:—Marsupium occupying pos- 
terior portion of outer gills, rather kidney-shaped, consisting of 
several ovisacs, twenty-five or thirty which, when gravid, extend 
far below the original edge, pigmented purplish ventrad; conglu- 
tinates white, not well formed, ova and glochidia discharged in 
rather loose masses; glochidium medium in size, semi-elliptic, 
rather short and straight, measures 0.210 x 0.265mm. 
SHELL STRUCTURES. 
EXTERNAL STRUCTURES:—Shell sub-elliptical, rather oblique, 
very solid, thick, heavy; ventral margin more rounded than 
dorsal; disk smooth; no post-umbonal ridge; rest lines of growth 
very distinct; .beaks projecting anteriorly, rather prominent, 
sculpturing indistinct; epidermis yellowish-horn color with green 
rays in young shell. 
INTERNAL STRUCTURES:—Cardinals very heavy, nearly par- 
allel to laterals with right post-cardinal converged dorsad and 
rounded up from a broad V-shaped gutter; interdentum broad, 
thick, right deeply gashed; beak cavities not very deep; nacre 
white, 
