136 THE AMERICAN MIDLAND NATURALIST 
INTERNAL STRUCTURES:—-Cardinals more or less double in 
both valves; laterals inclined to double also; umbonal cavities 
deep and rounded out; nacre white irridescent. 
Sex Length Height Diameter Um. ra. Locality 
QO -115' x 75° xX" 51mm’: x “o/2To' “(Lake Contrary, St. Joseph, Mon 
Cia 90n Xs OS x ah x 0.220 (Platte R., Agency Ford) 
SET OOmeks 70.0 Xa OE x 0.350 (Flat Creek, Sedalia, Mo.) 
OEEG6S. RPS aa ao 2O x 0.325 (Auxvasse R., Fulton, Mo.) 
fof Sine Kou) 555 Ac ude AN ay Xuowoo! wiGrancde ke Utica) 
The above measurement is the smallest ever taken by the 
author. It was discovered stranded on a sandbar, where it was 
traced by its tiny furrowed track in the fine wet sand. Although 
it had been but few days since its escape from its parasitic life 
on the fish, yet it had no byssi. It would seem from this, and many 
other instances, that neither the Unioninae nor Anodontinae develop 
byssal threads. Three other juveniles found on this same bar 
(measuring 11, 13 and 22 millimeters) were also devoid of byssi. 
It has been the author’s experience to find juveniles in companies. 
The juvenile quadrula has the general appearance of a young 
fragosa, having a straw-colored epidermis, very pointed posterior 
end, deeply sulcated post-ventral position, full rather double- 
apiculated beaks, with corrugated sculpturing and placed almost 
in the middle of the dorsal line; tubercles rather folded on anterior 
umbonal slopes ridged on post-umbonal slopes and finely ribbed 
on post-dorsal slopes. 
MISCELLANEOUS REMARKS:—Q. quadrula is represented by 
many forms in this state—especially in Central Missouri; how- 
ever, the large, heavy form that ranges from Ohio to Nebraska is 
rather constant in the drainage basins north of the Missouri 
River. It is strange that there should be such a depauperization 
of any of these forms in South Mo. This species is found in Arkan- 
sas but rather in the aspera form, a small quadrula such as mostly 
seen in the Osage system. Mr. Walker thinks that the key for 
tracing out the relative ranges of forms might be found in some 
ancient drainage system, and varieties, such as found in Missouri, 
ought to help solve the question. The inflated, solid and compara- 
tively smooth variety of Q. quarula of North Missouri may be 
referred to Pratt’s Udio lunulatus (Proc. Dav. Ac. Nat. Sci., I. 
1876, p. 167, Pl. XXXI, fig. 1). However, this may simply be 
the lacustrine form of the type since the fluviatile forms of North 
