340 THE AMERICAN MIDLAND NATURALIST 
- INTERNAL STRUCTURES :—Cardinals rather stumpy and stout; 
interdentum rather short and cut away; laterals very strong; 
nacre white with stippled effect—a very valuable shell com- 
mercially for this reason. 
Sex Length Height Diameter Locality , 
OVO Box SOSmex. 4qesmanm (Marais des Cygnes, Rich Hill) 
Sieumdoys Ioan) (se 128 Peslgiaehaol sn (Meramec R., Meramec Highlands) 
OP NCO) x MGC oS Setonnation (Osage R., Osceola) 
Sin 35h ke ee exe ev OF OLE (Gasconade R., Gascondy) 
U5 Seo Exe 8 Aeon (St. Francis R., Greenville) 
Sask Se Exes OMMt (St. Francis R., Greenvile). 
These last two measurements are those of two byssiferous 
quveniles identified by Dr. Howard and Prof. Clark. At first the 
writer was inclined to call them L. luteola chiefly on the grounds 
that both were found clinging by their byssi to a costata shell in 
a bed where /uteola predominated; however, this identification 
was excluded on the basis of the presence of anterior rays and a 
difference of umbonal sculpture being less prominent with the 
ridges more broken in case of juvenile ligamentina as shown in 
these two specimens. The byssus is attached to the upper posterior 
part of the foot although it extends out antero-ventrad between 
the valves. In the smaller juveniles the bysuss is about 120mm 
long, in the larger 135mm. Both bear dense papillae on both bran-. 
chial and anal openings. Anterior end of outer gills lifted up very 
high above the palpi, gills dark tan-color; branchial papillae rusty 
red; epidermis yellowish with bright broad green rays—mostly 
placed anteriorly. 
MIscELLANEOUS REMARKS:—While N. ligamentina may have 
the widest general distribution of the North American Nazades, 
yet it 7s not found anywhere in the interior of this State north of the 
Missouri River. However, it is the most common of species in 
the Mississippi, the Des Moines and in all the interior drainage 
south of the Missouri. It is not inclined to vary much from the 
typical ligamentina of Lamarck; however, the Osage River con- 
tains some forms that are somewhat puzzling due to ecological 
conditions that ercde the epidermis and distort the shell of this 
species (and of other characteristically rayed species, for that mat- 
ter), but these are of rare occurrence in the Osage from the center of 
its course to its mouth. As mentioned elsewhere this local effect 
may be traced to the chemical reaction of the mineral water of 
the springs’ region. There are no species it may be confused with 
