THE NAIADES OF MISSOURI 345 
that the sof parts are those of Nephronaias. The shell was 
identified later as ozarkensis of Call. 
SHELL CHARACTERS. 
EXTERNAL STRUCTURES :—Shell sub-elliptical, smooth, rather 
compressed; post-umbonal slope somewhat biangulate by siphonal 
ridges; beaks not prominent, sculptured by three fine undulations; 
epidermis brownish-yellow or olive with numerous fine green 
rays over central portion of disk; sexually dimophic. 
INTERNAL STRUCTURES:—Cardinals tend to double in both 
valves, laterals rather short, slightly curved; nacre usual'y white, 
sometimes salmon or pink, irridescent; muscle scars confluent. 
Sex Length Height Diameter Locality 
ONES OMx mas Ox, 21-0 (Jack’s Fork, Current R.) 
Cr 54n5 exe sey ke BL 5e2 (Jack’s Fork, Current R.) 
MISCELLANEOUS REMARKS:—The latter measurement is that 
of Call’s taken for a shell from the same locality (which is one of 
the type localities of ozarkensis) as for the shell of the first measure- 
ment which is now in the hands of the writer through the kindness 
of Mr. B. F. Bush, but which is now too much damaged through 
shipment for figuring. Its shell is very much like that of N. pleasi 
as to general outline, but is a little thicker and has a different 
nacre and epidermis. Forms of this Species reported by Meek 
and Clark (1912, p. 18) for the White River drainage and described 
as like ‘‘a very elongated Quadrula coccinea”’ and also identified 
by Mr. Walker as ‘‘Pleurobemae rather than species of Lamp- 
silis” are doubtless only Pleurobemae utterbackiu of Frierson. 
Definite assignment to the latter may be made for shells received 
from the White River, Hollister, Missouri, under the name of 
ozarkensis with the note:—‘‘although not having Lampsziline 
beak sculpture.’’ The reader is invited to compare descriptions 
and illustrations of Neph. ozarkensis and Pleu. utterbackw and note 
that the shell of the former does not possess such tumid beaks, 
nor such a furrowed post-slope, nor such distinct muscle scars, 
and its shell has its whole facies of a thinner, lighter character, 
thus being more inclined to a Lampsiline structure. 
Genus Amygdalonaias Crosse and Fischer. 
1893—Amygdalonaias Crosse and Fischer, Jour de Conch., pp. 31-32; 
1900b,—Simpson, Proc. U. S. Nat. Mus., XXII, p. 604 (as subgenus for 
Plagiola). 
