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THE NATURAL HISTORY SURVEY. 99 
29. Lampsilis gracilis Barnes, pl. xix., fig. 1. 
Unio gracilis BARNES, Amer. Journ. of Sci. and Arts, Ist series, Vol. VI., 
p. 274, 1823. 
Unio fragilis Ra¥., Conrad, Mon., pl. xxx., 18386. 
Unio dolosus Lea, Journ. Phil. Acad., Vol. V., p. 75, pl. ix., fig. 224, 1861. 
Shell; Elliptical, compressed, alate, rather thin; rounded 
before and very broadly rounded behind (sometimes obtusely 
triangular); dorsal margin straight, ventral margin rounded; 
dorsal margin alate posteriorly and the shell produced postero- 
ventrally; surface generally smooth and shining, the growth lines 
very faint, excepting on the alate portion; in old specimens the 
growth lines are more prominent; umbones very much de- 
pressed, light or dark horn color, marked by four wrinkles 
arranged in a double loop; in older specimens the umbones be- 
come almost smooth or are eroded; anterior umbonal slope 
almost flat, posterior slope long, subexcavated; ligament weak, 
long and narrow, very dark horn color; epidermis yellowish, 
with numerous grass green rays extending diagonally from the 
umbones to the base and posterior end; some specimens are 
plain yellow or yellowish horn; cardinal teeth weak, very thin, 
elevated, striated on the inner face, single in each valve, that in 
the right valve much the larger; Jateral teeth more solid than 
cardinals, long, lamellar, elevated, minutely striated, very 
slightly curved; no connecting plate between cardinal and lateral 
teeth; anterior adductor muscle scar longer than wide, im- 
pressed, striated; posterior adductor muscle scar very wide, not 
much impressed, confluent; protractor pedis muscle scar wider 
than long, impressed, striated; dorsal muscle scars arranged in 
almost a straight line under the cavity of the beaks, six to eleven 
in number in each valve, rather heavily impressed; cavity of the 
beaks very shallow; pallial line more or less distinct; nacre sil- 
very white, salmon tinged in the center of the shell, more or less 
iridescent. 
Length, 124.00; height, 78.00; breadth, 41.00 mill. (coll. Jensen). 
“ 88.00; oD 61.00; a 26.00 ‘'* (12945). 
Animal: Edges of anal opening very much thickened, with- 
out papille; branchial opening small, with large, irregular 
papille; mantle greatly thickened on its lower edge; palpi 
long, elliptical, united over half way behind; inner gill much the 
larger, rounded below, united the whole length of the abdominal 
sac; Marsupium enormous, with forty ovisacs, occupying the 
posterior three-fifths of the outer gill. (Simpson.) 
