NAIADES OF MISSOURI LQ 
or less parallel to post-ridges; beaks rather low and full, sculptured 
with numerous corrugated or double-looped ridges extending out 
as prominent nodules on the post-umbonal-looped ridges and 
zigzag, or WM-shaped, ridges on the umbonal region and upper 
part of disk; epidermis black, more or less dull color. 
INTERNAL STRUCTURES:—Cardinals moderately heavy, double 
in both valves; laterals very long, not much curved, interdentum 
- short, narrow; beak and branchial cavities rather deep; muscle 
scar—expecially the progressive impression and that of anterior 
retractor—very deep; nacre white (often with rusty spots) varying 
to pink. 
Sex Length Height Diameter Locality 
Oo 50") x 116 x, «56mm (Platte. R, Dixon Falls.) 
CHL Se Xe ekki nS; ter (WA ex ”  Garretsburg.) 
Sadia Siwy WSs) ok S00. (Osage R., Warsaw) 
OR 7 EU SS ti Kon 2 Sia (eas ” Monegaw Springs) 
Cis CAG eh 27 ee Xia 2, STG (hare ” Warsaw) 
OF e210) UeXaoy KOMP X OeSit (ine? a ETrOCtOr) 
The young and juvenile shells of the last two respec- 
tive measurements are very profusely sculptured—no part 
of the external surface being smooth—yet no undulations appear 
as seen in adult. Beaks low, corrugated; slopes of post-dorsal 
ridge finely costated; post-ridge with coarse, apiculated or spurred 
nodules; center and anterior of disk covered with irregularly 
placed V-shaped ridges and with scattered tubercles; valves 
extremely flat; nacre sky blue, irridescent. ‘‘ Work up old shells 
from the young ones”’ is Mr. Walker’s advice. 
MISCELLANEOUS REMARKS:—This most ponderous shell of 
the Naiades is typical in North Missouri and the Mississippi, 
but the typically massive shell is not found in Central Missouri, 
and, so far, it is not reported at all for the southern slope of the 
Ozarks in this state. As a rule, heros is only found in the large 
rivers; however, in this State the type is found in the Missouri 
Platte—a rather small river, while the medium sized one is found 
in the largest river of the interior—the Osage—where it assumes 
the small form perhaps approaching that of dombeyana Valen- 
ciennes. ‘‘Giant heros,’’ as this species is often called, is most 
frequently found in the deepest depressions of mud bottom with 
a substratum of solid limestone. It hardly ever moves from these 
situations and perhaps because of this inactivity it accumulates 
its heavy shell, Because of the following peculiar characters the 
