| igh ig? THE AMERICAN MIDLAND NATURALIST 
times shows a tendency to bianguation posteriorly; beaks incurved, 
projecting forward, sculptured with concentric lines but no sculp- 
turing carried out on the disk; rest lines of growth concentric 
and furrowed; epidermis satiny horn color. 
INTERNAL STRUCTURES:—Cardinals large and massive; lat- 
erals long and heavy; interdentum broad; beak cavities deeply 
creviced; scars deep; nacre pure white, stippled, irridescent. 
Sex Length Height Diameter Um. ra. Locality. 
CuaerOsh: (Xa 77509 (X Oomim 0.090 . (Miss. R., La Grange, Mo.) 
9 95) x) 65. xe (572mm 0.100 ay he? rs Shia Vad 0k 5) 
oo) 56> x 46) (x {32mm 0.120 (7. Hannibal, Mo.) 
fot 20.5%) 1S) X 8mm O.115 (UR tes a 2) 
The shell of the juvenile of this last measurment is so round, 
and with beaks so drawn up to center of dorsal line that it resembles 
that of a Sphaertum. Umbonal sculpturing not very distinct 
even in this juvenile. It can always be identified in the early 
stages of its juvenility by white spots located post-dorsad on its 
shell. 
MISCELLANEOUS REMARKS:—The writer, after some years of 
extensive collecting from the largest streams of the state, has 
failed to find ebena in the interior streams, neither have any Mis- 
souri collectors, nor old ‘‘clammers’’ reported it. This shell is 
known not only for its greatest commercial value and for its rarity 
in general geographical distribution but also for its great abundance 
locally. Of course its only home, known so far, is the Mississippi 
north of the Missouri River. It is not known why this species 
does not occur for this state in those Ozark rivers that bear it in 
great abundance in Arkansas not far from the Missouri-Arkansas 
line. Sometimes a black shelled Pleurobema pyramidatum or 
Fusconaia undata trigonoides may be taken for the ‘‘ Nigger Head”’ 
(F. ebena), but, from the characteristic cornucopia-form of shell, 
together with its deep brown satiny epidermis and regular, con- 
centric furrowed rest lines of growth, it should be easily identified. 
Frierson reports ebena as a rare shell in Louisiana and Isely (1914, 
pp. 1-4) does not report it at all for the Arkansas and Red River 
drainages of eastern Oklahoma. Perhaps Call’s account of it (1895, 
p- 16) as a common shell, not only for Arkansas, but for all the 
larger rivers west of the Mississippi, is more conjectured than 
real. Its breeding season has been found by Wilson and Clark 
(1914, p. 42) to extend from May to the middle of July. Surber 
