THE NAIADES OF MISSOURI 93 



Genus Uniomerus Conrad. 



1853 — Uniomerus Conrad, Proc. Ac. Nat. Sci. Phila, VI, p. 268. (as 



genus). 

 1900b — Uniomerus (Conrad) Simpson, Proc. U. S. Nat. Mus., XXII, 



P- 739 (as section). 



(Type, Unio tetralasmus Say). 



Animal Characters: — Both branchial and anal openings 

 papillose and crenulate; supra-anal closely and loosely connected 

 to anal ; inner laminae of inner gills free from the visceral mass 

 almost their full length; papli short almost as wide as long; color 

 of soft parts mostly a soiled white, gills brownish; gills only mar- 

 supial in outer ones, when gravid rather distended lengthwise 

 in center, tapering at the ventral edge, ovisacs not divided; septa 

 wavy; conglutinates white, sole-shaped; glochidia medium in 

 size, semielliptical, higher than long, hinge line straight. 



Shell Characters : — Shell trapezoidal, rather obtusely 

 pointed behind; disk smooth with the exception of roughened 

 growth lines; beaks low, sculptured with several coarse concentric 

 ridges which curve abruptly upward behind where they are 

 crowded closely together; epidermis rayless, shiny, yellowish 

 to black; cardinals compressed; laterals nearly straight; nacre 

 whitish to bluish. 



Miscellaneous Remarks: — Dr. Ortmann elevates Unio- 

 merus from Simpson's treatment of it as section mostly because of 

 the peculiar beak sculpture of its type since this character alone 

 is a great departure from the Elliptio-sheW (See Plate xxi, fig. 6g). 

 Then, too, the shell is thinner, has more of a rayless, vari-colored 

 polished epidermis and is more elongated with less curved dorsal 

 or ventral line. 



TJniomerus tetralasmus (Say). 



(^Pond Horn Shell.") 

 PL XXI, Figs. 69 A and B. 

 1830 — Unio tetralasmus Say, Am. Conch., Ill, pi. XXIII. . ''^\ 



1836 — Unio declivis Conrad, Monog., V, p. 45, pi. XXIII, fig. i. 

 1839 — Unio sayi Ward, (in Tappan). Am. Jl. Sd., XXXV, p. 26S, 

 pi. Ill, fig. I. 



