98 THE AMERICAN MIDLAND NATURALIST 
outer, inter-laminar connections not irregularly distributed but 
arranged obliquely parallel to each other, outer lamina of outer 
gill free from mantle posteriorly, inner lamina of inner gill almost 
entirely free from visceral mass; all four gills marsupial; anterior 
adductors reinforced posteriorly. 
SHELL CHARACTERS:—Shell narrowly elliptical, no sculpture 
on disk, low beaks scuptured with ridges parallel with growth 
lines; epidermis black; anterior cardinals lacking, posterior 
ones conical; anterior adductor muscle scar deeply impressed 
post-dorsad; nacre pearl blue to white. 
Cumberlandia monodonta (Say). 
(‘‘Spectacle Case.’’) 
PIX Vis Pes: 28A> and se. 
1829— Unio monodonta Say, N. Harm. Diss., IIp. 293; 1830, Am. 
Concha eeie vil 
1853— Margaritana monodonta Conrad, Pr. Ac. N. Sci., Phila. VI, p 262. 
1912a—Cumberlandia monodonta Ortmann, Nautilus XXVI, pp 13 
and 14. 
AVS r. 
Fic. 1.—Cumberlandia monodonta (Say). 9 Diagram of sterile indi- 
vidual from the Osage River, Sagrada, Mo., showing animal 
characters in left valve. (Nat. size.) 
ANIMAL CHARACTERS. 
NUTRITIVE STRUCTURES:—Branchial opening with papillae 
reduced to mere crenulations; no gill partition (diaphragm) 
between branchial and anal openings; no true supra-anal opening; 
gills very long and narrow with interlaminar connections regularly 
arranged as ‘‘continuous septa which run obliquely forwards;”’ 
inner lamina of inner gill free from visceral mass except at its 
