THE NAIADES OF MISSOURI 131 



described above and is not often seen among the Naiades. In 

 that there are not such advantages for the aeration 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.") 



PI. XXV, Figs. 82 A—F. 



1820 — Obliquaria (Quadrula) reflexa Rafinesque, Ann. Gen. Sci. Phys., 

 p. 306; Chenu. Bib. Conch., ist ser., Ill, 1845, p. 19. 



1823 — Unto cornutus Barnes, Am. Jl. Sci., VI, p. 122, pi. 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 vStructures: — 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- 



