THE NAIADES OF MISSOURI 319 
described above and is not often seen among the Nazades. In 
that there are not such advantages for the aération of the embryos 
and also a greater reduction in the number of ovisacs as seen in 
most other genera of this sub-family, this genus is given a primitive 
grouping here. However, in the reduction of the number of ovisacs 
a compensation is made in the enlargement and elongation. This 
genus has a rather wide distribution over the northern and central 
parts of the state, but is entirely absent from the drainage of the 
south slope of the Ozarks. 
Obliquaria reflexa Rafinesque. 
(‘‘Horny-Back,’’ ‘‘Three-Horned Warty-Back.’’) 
Pl. XXV, Figs. 82 A—F. 
1820—Obliquaria (Quadrula) reflexa Rafinesque, Ann. Gen. Sci. Phys., 
p. 306; Chenu. Bib. Conch., 1st ser., III, 1845, p. 19. 
1823— Unio cornutus Barnes, Am. Jl. Sci., VI, p. 122, pl. IV, fig. 5. 
1900b—Obliquaria reflexa (Raf.) Simpson, Proc. U. S. Nat. Mus., 
XXII, p. 611; Ortmann 1912b—An. Car. Mus., VIII, pp. 310-312. 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES :— Branchial opening large with light 
colored papillae on a black back-ground; anal crenulated; supra- 
anal rather large and briefly connected to anal; inner laminae of 
inner gills free except for a short distance anteriorly; palpi small, 
wide, short, connected for one-half of their length antero-dorsad; 
color of soft parts grayish or dirty white, mantle edges at branchial 
opening black, branchial papillae and inner margin of anal opening 
yellowish, gills of male and sterile female tan-color. 
REPRODUCTIVE STRUCTURES:—Only outer gills marsupial, 
when sterile, the ovisacs not extending below edge of gill, when 
gravid larger and greatly elongated beyond the original edge, 
ovisacs 5-7 in number, large, club-shaped, curved post-ventrad, 
glochidia scattered throughout the conglutinated mass; conglu- 
tinates club-shaped, solid, white, discharged whole; glochidia 
semi-circular, medium in size, hinge line slightly curved upward 
in middle, measures 0.225 x 0.235mm. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES:—Shell sub-trigonal, heavy and thick 
anteriorly, post-dorsal line rounded; slightly incurved post- 
