1 6 NAIADES OF MISSOURI 



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. 



SheIvIv 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.") 



PL XV. Figs. 28 A and B. 



1829 — Unio monodonta Say, N. Harm. Diss., Up. 293; 1830, Am. 



Conch I. PI. VI. 

 1853 — Margaritana monodonta Conrad, Pr. Ac. N. Sci., Phila. VI, p 262. 

 1912a — Cumberlandia monodonta Ortmann, Nautilus XXVI, pp 13 



and 14. 



Fig. I. — 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 



