202 NEW-YORK FAUNA — MOLLUSCA. 
ANODON EXCURVATA. 
PLATE XVII. FIG. 233. 
(STATE COLLECTION.) 
Description. Shell thin and fragile, transversely oblong, inflated, cylindrical. Beaks slightly 
before the anterior third of the shell, prominent, decorticated (in young shells with two or 
three distant undulations), the greatest thickness at the middle of the shell. Hinge-margin 
short, straight, forming a descending slope posteriorly, broadly emarginate beyond ; this is 
more obvious in the younger shells, in which the hinge-slope is more elevated: the ridge 
from the beaks distinct and rounded, including two concentric elevations on each side ; the 
posterior end produced, obtusely pointed, upturned: basal margin, in adults, slightly con- 
tracted in the middle. Surface deeply corrugated by the lines of growth, and these corruga- 
tions are distinctly marked within. 
Color. Epidermis varying from light grass-green in the young, to deeper green and oliva- 
ceous in the adult, with narrow obscure greenish radiations, often minutely wrinkled : interior 
bluish iridescent, with a faint tinge in some of salmon towards the cavity of the beaks. In 
adults, the interior is strongly impressed by some of the stages of growth. 
Vertical axis, 2.7; transverse ditto, 5°5. Diameter, 2°1. 
This superb Anodon was found by Dr. W. Newcomb in Shaker pond, Niskayuna, Albany 
county, and by Mr. Cozzens in the Passaic river in the neighborhood of this city. Its size, 
almost cylindrical shape, with its peculiar upturned posterior extremity, could not be recon- 
ciled to any of the descriptions accessible to me. It seems most allied to the zmplicata of 
Say, but the description and figure do not apply to this. ‘The young are not so much inflated. 
In one whose transverse axis was 2°4, the vertical axis was 1°2, and the diameter only 0°8. 
In the collection of Dr. Budd, are specimens from Lake Champlain, which I refer to this 
species ; in the greater part of these, the beaks and the ridge to the posterior margin of the 
shell are of an orange, or rather of a mahogany color, which is more or less diffused over 
the shell. 
ANODON IMPLICATA. 
Anodonta implicata, Say, Des. terr. & fluv. Shells, p. 21. Russet, Essex Jour. Vol. 2, p. 60. 
A. newtoniensis. Lea, Trans. Am, Phil. Soc. Vol. 6, p. 79, pl. 21, fig. 66, fide Gould. 
A. marginata (young). Say, Nich. Ency. Vol. 4, pl. 3, fig. 5. 
A. implicata. Gouwr, Invertebrata of Mass. p. 118, fig. 78, 
Description. Shell thick, strong and heavy, subcylindrical, suboval. Beaks somewhat 
elevated at the anterior two-fifths ; breadth greatest behind the middle : ridge from the beaks 
to the posterior margin very distinct and prominent ; the margin itself bluntly rounded, not 
upturned : in the space above this, are three or four coarse concentric lines ; basal margin 
deeply arched, and contracted in large specimens. Surface roughened by the irregular stages 
of growth. 
